Preoperatively planning an arthroplasty procedure and generating a corresponding patient specific arthroplasty resection guide

ABSTRACT

A method of manufacturing an arthroplasty jig is disclosed herein. The method may include the following: generate two dimensional image data of a patient joint to undergo arthroplasty, identify in the two dimensional image data a first point corresponding to an articular surface of a bone forming the joint, identify a second point corresponding to an articular surface of an implant, identify a location of a resection plane when the first point is correlated with the second point, and create the arthroplasty jig with a resection guide located according to the identified location of the resection plane.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 14/084,255 filed Nov. 19, 2013, which application is acontinuation of U.S. patent application Ser. No. 13/086,275 (“the '275application”), filed Apr. 13, 2011, and titled “Preoperatively Planningan Arthroplasty Procedure and Generating a Corresponding PatientSpecific Arthroplasty Resection Guide,” now U.S. Pat. No. 8,617,171. The'275 application is a continuation-in-part (“CIP”) of U.S. patentapplication Ser. No. 12/760,388 (“the '388 application”), filed Apr. 14,2010, now U.S. Pat. No. 8,737,700.

The '388 application is a CIP application of U.S. patent applicationSer. No. 12/563,809 (“the '809 application), filed Sep. 21, 2009, andtitled “Arthroplasty System and Related Methods.” now U.S. Pat. No.8,545,509, which claims priority to U.S. patent application 61/102,692(“the '692 application”), filed Oct. 3, 2008, and titled “ArthroplastySystem and Related Methods.” The '388 application is also a CIPapplication of U.S. patent application Ser. No. 12/546,545 (“the 545application”), filed Aug. 24, 2009, and titled “Arthroplasty System andRelated Methods.” now U.S. Pat. No. 8,715,291, which claims priority tothe '692 application.

The '545 application is also a CIP application of U.S. patentapplication Ser. No. 12/111,924 (“the '924 application”), filed Apr. 29,2008, and titled “Generation of a Computerized Bone Model Representativeof a Pre-Degenerated State and Useable in the Design and Manufacture ofArthroplasty Devices,” now U.S. Pat. No. 8,480,679. The '545 applicationis also a CIP application of U.S. patent application Ser. No. 11/959,344(“the '344 application), filed Dec. 18, 2007, and titled “System andMethod for Manufacturing Arthroplasty Jigs.” now U.S. Pat. No.8,221,430.

The '809 application is a CIP application of U.S. patent applicationSer. No. 12/505,056 (“the '056 application”), filed Jul. 17, 2009, andtitled “System and Method for Manufacturing Arthroplasty Jigs HavingImproved Mating Accuracy.” now U.S. Pat. No. 8,777,875. The '056application claims priority to U.S. patent application 61/083,053, filedJul. 23, 2008, and titled “System and Method for ManufacturingArthroplasty Jigs Having Improved Mating Accuracy.” The '809 applicationis also a CIP application of the '924 application. The '809 applicationis also a CIP application of the '344 application.

The present application claims priority to all of the above mentionedapplications and hereby incorporates by reference all of theabove-mentioned applications in their entireties into the presentapplication.

FIELD OF THE INVENTION

The present invention relates to customized arthroplasty cutting jigs.More specifically, the present invention relates to systems and methodsof manufacturing such jigs.

BACKGROUND OF THE INVENTION

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on hones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., arthritis) can cause cartilage in joint areas, which normallyprovides a cushioning effect, to wear down. When the cartilage wearsdown, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility.

Arthroplasty procedures can be used to repair damaged joints. During atypical arthroplasty procedure, an arthritic or otherwise dysfunctionaljoint can be remodeled or realigned, or an implant can be implanted intothe damaged region. Arthroplasty procedures may take place in any of anumber of different regions of the body, such as a knee, a hip, ashoulder, or an elbow.

One type of arthroplasty procedure is a total knee arthroplasty (“TKA”),in which a damaged knee joint is replaced with prosthetic implants. Theknee joint may have been damaged by, for example, arthritis (e.g.,severe osteoarthritis or degenerative arthritis), trauma, or a raredestructive joint disease. During a TKA procedure, a damaged portion inthe distal region of the femur may be removed and replaced with a metalshell, and a damaged portion in the proximal region of the tibia may beremoved and replaced with a channeled piece of plastic having a metalstem. In some TKA procedures, a plastic button may also be added underthe surface of the patella, depending on the condition of the patella.

Implants that are implanted into a damaged region may provide supportand structure to the damaged region, and may help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of animplant in a damaged region, the damaged region may be prepared toreceive the implant. For example, in a knee arthroplasty procedure, oneor more of the bones in the knee area, such as the femur and/or thetibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) toprovide one or more surfaces that can align with the implant and therebyaccommodate the implant.

Accuracy in implant alignment is an important factor to the success of aTKA procedure. A one- to two-millimeter translational misalignment, or aone- to two-degree rotational misalignment, may result in imbalancedligaments, and may thereby significantly affect the outcome of the TKAprocedure. For example, implant misalignment may result in intolerablepost-surgery pain, and also may prevent the patient from having full legextension and stable leg flexion.

To achieve accurate implant alignment, prior to treating (e.g., cutting,drilling, reaming, and/or resurfacing) any regions of a bone, it isimportant to correctly determine the location at which the treatmentwill take place and how the treatment will be oriented. In some methods,an arthroplasty jig may be used to accurately position and orient afinishing instrument, such as a cutting, drilling, reaming, orresurfacing instrument on the regions of the bone. The arthroplasty jigmay, for example, include one or more apertures and/or slots that areconfigured to accept such an instrument.

A system and method has been developed for producing customizedarthroplasty jigs configured to allow a surgeon to accurately andquickly perform an arthroplasty procedure that restores thepre-deterioration alignment of the joint, thereby improving the successrate of such procedures. Specifically, the customized arthroplasty jigsare indexed such that they matingly receive the regions of the bone tobe subjected to a treatment (e.g., cutting, drilling, reaming, and/orresurfacing). The customized arthroplasty jigs are also indexed toprovide the proper location and orientation of the treatment relative tothe regions of the bone. The indexing aspect of the customizedarthroplasty jigs allows the treatment of the bone regions to be donequickly and with a high degree of accuracy that will allow the implantsto restore the patient's joint to a generally pre-deteriorated state.However, the system and method for generating the customized jigs mayrely on a plurality of images from a MRI scan or CT scan to construct a3D bone model. The image slice orientation of the MRI scan or CT scan isat least partially dependent upon the imaging system operator to placethe localizer in various positions during the scan. This imaging processis subject to operator error, such as inaccurate placement of thelocalizer, thereby increasing the time, manpower and costs associatedwith producing the customized arthroplasty jig.

There is a need in the art for a system and method for reducing thelabor associated with generating customized arthroplasty jigs. There isalso a need in the art for a system and method for reducing the effectsof operator error and thereby increasing the accuracy of customizedarthroplasty jigs.

SUMMARY

Various embodiments of a method of manufacturing an arthroplasty jig aredisclosed herein. In a first embodiment, the method may include thefollowing: generate two dimensional image data of a patient joint toundergo arthroplasty, identify in the two dimensional image data a firstpoint corresponding to an articular surface of a bone forming the joint,identify a second point corresponding to an articular surface of animplant, identify a location of a resection plane when the first pointis correlated with the second point, and create the arthroplasty jigwith a resection guide located according to the identified location ofthe resection plane.

In a second embodiment, the method may include the following: (a)identify a first attribute in a coronal image and a second attribute inan axial image, wherein the attributes are associated with a boneforming a portion of a patient joint, (b) place the first and secondattributes in a sagittal relationship, (c) compare in the sagittalrelationship the first and second attributes to respective correspondingattributes of a plurality of candidate prosthetic implants, (d) select aprosthetic implant from the comparison of step c, (e) correlate in thesagittal relationship the first and second attributes to respectivecorresponding attributes of the prosthetic implant, (f) identify thelocation of a resection plane associated with the prosthetic implantduring the correlation of step e, and (g) create the arthroplasty jigwith a resection guide located according to the identified location ofthe resection plane.

In a third embodiment, the method may include the following: (a)identify first and second attributes in a sagittal image, wherein theattributes are associated with a bone forming a portion of a patientjoint, (b) place the first and second attributes in an axialrelationship, (c) compare in the axial relationship the first and secondattributes to respective corresponding attributes of a plurality ofcandidate prosthetic implants, (d) select a prosthetic implant from thecomparison of step c, (e) correlate in the axial relationship the firstand second attributes to respective corresponding attributes of theprosthetic implant, (f) identify the location of a resection planeassociated with the prosthetic implant during the correlation of step e,and (g) create the arthroplasty jig with a resection guide locatedaccording to the identified location of the resection plane.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a system for employing the automatedjig production method disclosed herein.

FIGS. 1B-1E are flow chart diagrams outlining the jig production methoddisclosed herein.

FIGS. 2A and 2B are, respectively, bottom and top perspective views ofan example customized arthroplasty femur jig.

FIGS. 2C and 2D are, respectively, top/posterior and bottom/anteriorperspective views of an example customized arthroplasty tibia jig.

FIG. 3A is an isometric view of a 3D computer model of a femur lower endand a 3D computer model of a tibia upper end in position relative toeach to form a knee joint and representative of the femur and tibia in anon-degenerated state.

FIG. 3B is an isometric view of a 3D computer model of a femur implantand a 3D computer model of a tibia implant in position relative to eachto form an artificial knee joint.

FIG. 4 is a perspective view of the distal end of 3D model of the femurwherein the femur reference data is shown.

FIG. 5A is a sagittal view of a femur illustrating the orders andorientations of imaging slices utilized in the femur POP.

FIG. 5B depicts axial imaging slices taken along section lines of thefemur of FIG. 5A.

FIG. 5C depicts coronal imaging slices taken along section lines of thefemur of FIG. 5A.

FIG. 6A is an axial imaging slice taken along section lines of the femurof FIG. 5A, wherein the distal reference points are shown.

FIG. 6B is an axial imaging slice taken along section lines of the femurof FIG. 5A, wherein the trochlear groove bisector line is shown.

FIG. 6C is an axial imaging slice taken along section lines of the femurof FIG. 5A, wherein the femur reference data is shown.

FIG. 6D is the axial imaging slices taken along section lines of thefemur in FIG. 5A.

FIG. 7A is a coronal slice taken along section lines of the femur ofFIG. 5A, wherein the femur reference data is shown

FIG. 7B is the coronal imaging slices taken along section lines of thefemur in FIG. 5A.

FIG. 7C is a sagittal imaging slice of the femur in FIG. 5A.

FIG. 7D is an axial imaging slice taken along section lines of the femurof FIG. 5A, wherein the femur reference data is shown.

FIG. 7E is a coronal imaging slice taken along section lines of thefemur of FIG. 5A, wherein the femur reference data is shown.

FIG. 8 is a posterior view of a 3D model of a distal femur.

FIG. 9 depicts a y-z coordinate system wherein the femur reference datais shown.

FIG. 10 is a perspective view of a femoral implant model, wherein thefemur implant reference data is shown.

FIG. 11 is another perspective view of a femoral implant model, whereinthe femur implant reference data is shown.

FIG. 12 is a y-z coordinate system wherein some of the femur implantreference data is shown.

FIG. 13 is an x-y-z coordinate system wherein the femur implantreference data is shown.

FIG. 14A shows the femoral condyle and the proximal tibia of the knee ina sagittal view MRI image slice.

FIG. 14B is a coronal view of a knee model in extension.

FIGS. 14C and 14D illustrate MRI segmentation slices for joint lineassessment.

FIG. 14E is a flow chart illustrating the method for determiningcartilage thickness used to determine proper joint line.

FIG. 14F illustrates a MRI segmentation slice for joint line assessment.

FIGS. 14G and 14H illustrate coronal views of the bone images in theiralignment relative to each as a result of OA.

FIG. 14I illustrates a coronal view of the bone images with a restoredgap Gp3.

FIG. 14J is a coronal view of bone images oriented relative to eachother in a deteriorated state orientation.

FIG. 15 is a 3D coordinate system wherein the femur reference data isshown.

FIG. 16 is a y-z plane wherein the joint compensation points are shown.

FIG. 17 illustrates the implant model 34′ placed onto the samecoordinate plane with the femur reference data.

FIG. 18A is a plan view of the joint side of the femur implant modeldepicted in FIG. 3B.

FIG. 18B is an axial end view of the femur lower end of the femur bonemodel depicted in FIG. 3A.

FIG. 18C illustrates the implant extents iAP and iML and the femurextents bAP, bML as they may be aligned for proper implant placement.

FIG. 19A shows the most medial edge of the femur in a 2D sagittalimaging slice.

FIG. 19B, illustrates the most lateral edge of the femur in a 2Dsagittal imaging slice.

FIG. 19C is a 2D imaging slice in coronal view showing the medial andlateral edges.

FIG. 20A is a candidate implant model mapped onto a y-z plane.

FIG. 20B is the silhouette curve of the articular surface of thecandidate implant model.

FIG. 20C is the silhouette curve of the candidate implant model alignedwith the joint spacing compensation points D_(1J)D_(2J) andP_(1J)P_(2J).

FIG. 21A illustrates a sagittal imaging slice of a distal femur with animplant model.

FIG. 21B depicts a femur implant model wherein the flange point on theimplant is shown.

FIG. 21C shows an imaging slice of the distal femur in the sagittalview, wherein the inflection point located on the anterior shaft of thespline is shown.

FIG. 21D illustrates the 2D implant model properly positioned on the 2Dfemur image, as depicted in a sagittal view.

FIG. 22A depicts an implant model that is improperly aligned on a 2Dfemur image, as depicted in a sagittal view.

FIG. 22B illustrates the implant positioned on a femur transform whereina femur cut plane is shown, as depicted in a sagittal view.

FIG. 23 is a top view of the tibia plateaus of a tibia bone image ormodel.

FIG. 24A is a sagittal cross section through a lateral tibia plateau ofthe 2D tibia bone model or image.

FIG. 24B is a sagittal cross section through a medial tibia plateau ofthe 2D tibia bone model or image.

FIG. 24C depicts a sagittal cross section through an undamaged or littledamaged medial tibia plateau of the 2D tibia model wherein osteophytesare also shown.

FIG. 24D is a sagittal cross section through a damaged lateral tibiaplateau of the 2D tibia model.

FIG. 25A is a coronal 2D imaging slice of the tibia.

FIG. 25B is an axial 2D imaging slice of the tibia.

FIG. 26A depicts the tibia reference data on an x-y coordinate system.

FIG. 26B depicts the tibia reference data on a proximal end of the tibiato aid in the selection of an appropriate tibia implant.

FIG. 27A is a 2D sagittal imaging slice of the tibia wherein asegmentation spline with an AP extant is shown.

FIG. 27B is an axial end view of the tibia upper end of the tibia bonemodel depicted in FIG. 3A.

FIG. 27C is a plan view of the joint side of the tibia implant modeldepicted in FIG. 3B.

FIG. 28 is a top isometric view of the tibia plateaus of a tibia implantmodel.

FIG. 29A is an isometric view of the 3D tibia bone model showing thesurgical cut plane SCP design.

FIGS. 29B and 29C are sagittal MRI views of the surgical tibia cut planeSCP design with the posterior cruciate ligament PCL.

FIG. 30A is an isometric view of the tibia implant wherein a cut planeis shown.

FIG. 30B is a top axial view of the implant superimposed on the tibiareference data.

FIG. 30C is an axial view of the tibial implant aligned with the tibiareference data.

FIG. 30D is a MRI imaging slice of the medial portion of the proximaltibia and indicates the establishment of landmarks for the tibia POPdesign, as depicted in a sagittal view.

FIG. 30E is a MRI imaging slice of the lateral portion of the proximaltibia, as depicted in a sagittal view.

FIG. 30F is an isometric view of the 3D model of the tibia implant andthe cut plane.

FIGS. 31A1-31A2 are sagittal views of a 2D imaging slice of the femurwherein the 2D computer generated implant models are also shown.

FIG. 31B is a sagittal view of a 2D imaging slice of the tibia whereinthe 2D computer generated implant model is also shown.

FIGS. 32A-32C are various views of the 2D implant models superimposed onthe 2D bone models.

FIG. 32D is a coronal view of the 2D bone models.

FIGS. 32E-32G are various views of the 2D implant models superimposed onthe 2D bone models.

FIG. 33A is a medial view of the 3D bone models.

FIG. 33B is a medial view of the 3D implant models

FIG. 33C is a medial view of the 3D implant models superimposed on the3D bone models.

FIGS. 34A-35B illustrate isometric views of embodiments of thearthroplasty jigs configured to provide natural alignment resections,zero degree mechanical axis alignment resections, and resectionsresulting in alignments between zero degree mechanical axis alignmentand natural alignment.

DETAILED DESCRIPTION

Disclosed herein are customized arthroplasty jigs 2 and systems 4 for,and methods of, producing such jigs 2. The jigs 2 are customized to fitspecific bone surfaces of specific patients. Depending on theembodiment, the jigs 2 are automatically planned and generated and maybe similar to those disclosed in these three U.S. patent applications:U.S. patent application Ser. No. 11/656,323 to Park et al., titled“Arthroplasty Devices and Related Methods” and filed Jan. 19, 2007, nowU.S. Pat. No. 9,017,336; U.S. patent application Ser. No. 10/146,862 toPark et al., titled “Improved Total Joint Arthroplasty System” and filedMay 15, 2002; and U.S. patent Ser. No. 11/642,385 to Park et al., titled“Arthroplasty Devices and Related Methods” and filed Dec. 19, 2006. Thedisclosures of these three U.S. patent applications are incorporated byreference in their entireties into this Detailed Description.

A. Overview of System and Method for Manufacturing CustomizedArthroplasty Cutting Jigs

For an overview discussion of the systems 4 for, and methods of,producing the customized arthroplasty jigs 2, reference is made to FIGS.1A-1E. FIG. 1A is a schematic diagram of a system 4 for employing theautomated jig production method disclosed herein. FIGS. 1B-1E are flowchart diagrams outlining the jig production method disclosed herein. Thefollowing overview discussion can be broken down into three sections.

The first section, which is discussed with respect to FIG. 1A and[blocks 100-125] of FIGS. 1B, 1C1, 1C2, and 1E, pertains to an examplemethod of determining, in a two-dimensional (“2D”) computer modelenvironment, saw cut and drill hole locations 30, 32 relative to 2Dimages 16 of a patient's joint 14. The resulting “saw cut and drill holedata” 44 is planned to provide saw cuts 30 and drill holes 32 that willallow arthroplasty implants to restore the patient's joint to itspre-degenerated or natural alignment state.

The second section, which is discussed with respect to FIG. 1A and[blocks 100-105 and 130-145] of FIGS. 1B, 1D, and 1E, pertains to anexample method of importing into 3D computer generated jig models 38 3Dcomputer generated surface models 40 of arthroplasty target areas 42 of3D computer generated arthritic models 36 of the patient's joint bones.The resulting “jig data” 46 is used to produce a jig customized tomatingly receive the arthroplasty target areas of the respective bonesof the patient's joint.

The third section, which is discussed with respect to FIG. 1A and[blocks 150-165] of FIG. 1E, pertains to a method of combining orintegrating the “saw cut and drill hole data” 44 with the “jig data” 46to result in “integrated jig data” 48. The “integrated jig data” 48 isprovided to the CNC machine 10 or other rapid production machine (e.g.,a stereolithography apparatus (“SLA”) machine) for the production ofcustomized arthroplasty jigs 2 from jig blanks 50 provided to the CNCmachine 10. The resulting customized arthroplasty jigs 2 include saw cutslots and drill holes positioned in the jigs 2 such that when the jigs 2matingly receive the arthroplasty target areas of the patient's bones,the cut slots and drill holes facilitate preparing the arthroplastytarget areas in a manner that allows the arthroplasty joint implants togenerally restore the patient's joint line to its pre-degenerated stateor natural alignment state.

As shown in FIG. 1A, the system 4 includes a computer 6 having a CPU 7,a monitor or screen 9 and an operator interface controls 11. Thecomputer 6 is linked to a medical imaging system 8, such as a CT or MRImachine 8, and a computer controlled machining system 10, such as a CNCmilling machine 10.

As indicated in FIG. 1A, a patient 12 has a joint 14 (e.g., a knee,elbow, ankle, wrist, hip, shoulder, skull/vertebrae orvertebrae/vertebrae interface, etc.) to be replaced. The patient 12 hasthe joint 14 scanned in the imaging machine 8. The imaging machine 8makes a plurality of scans of the joint 14, wherein each scan pertainsto a thin slice of the joint 14.

As can be understood from FIG. 1B, the plurality of scans is used togenerate a plurality of two-dimensional (“2D”) images 16 of the joint 14[block 100]. Where, for example, the joint 14 is a knee 14, the 2Dimages will be of the femur 18 and tibia 20. The imaging may beperformed via CT or MRI. In one embodiment employing MRI, the imagingprocess may be as disclosed in U.S. patent application Ser. No.11/946,002 to Park, which is entitled “Generating MRI Images Usable ForThe Creation Of 3D Bone Models Employed To Make Customized ArthroplastyJigs,” was filed Nov. 27, 2007 and is incorporated by reference in itsentirety into this Detailed Description. The images 16 may be a varietyof orientations, including, for example, sagittal 2D images, coronal 2Dimages and axial 2D images.

As can be understood from FIG. 1A, the 2D images are sent to thecomputer 6 for analysis and for creating computer generated 2D modelsand 3D models. In one embodiment, the bone surface contour lines of thebones 18, 20 depicted in the image slices 16 may be auto segmented viaan image segmentation process as disclosed in U.S. Patent Application61/126,102, which was filed Apr. 30, 2008, is entitled System and Methodfor Image Segmentation in Generating Computer Models of a Joint toUndergo Arthroplasty, and is hereby incorporated by reference into thepresent application in its entirety.

As indicated in FIG. 1B, in one embodiment, reference point W isidentified in the 2D images 16 [block 105]. In one embodiment, asindicated in [block 105] of FIG. 1A, reference point W may be at theapproximate medial-lateral and anterior-posterior center of thepatient's joint 14. In other embodiments, reference point W may be atany other location in the 2D images 16, including anywhere on, near oraway from the bones 18, 20 or the joint 14 formed by the bones 18, 20.Reference point W may be defined at coordinates (X_(0-j), Y_(0-j),Z_(0-j)) relative to an origin (X₀, Y₀, Z₀) of an X-Y-Z axis anddepicted in FIGS. 1B-1D as W (X_(0-j), Y_(0-j), Z_(0-j)). Throughout theprocesses described herein, to allow for correlation between thedifferent types of images, models or any other data created from theimages, movements of such images, models or any other data created formthe images may be tracked and correlated relative to the origin.

As described later in this overview, point W may be used to locate the2D images 16 and computer generated 3D model 36 created from the 2Dimages 16 respectively with the implant images 34 and jig blank model 38and to integrate information generated via the POP process. Depending onthe embodiment, point W, which serves as a position and/or orientationreference, may be a single point, two points, three points, a point plusa plane, a vector, etc., so long as the reference point W can be used toposition and/or orient the 2D images 16, 34 and 3D models 36, 38relative to each other as needed during the POP process.

As shown in FIG. 1C1, the coronal and axial 2D images 16 of the femur 18forming the patient's joint 14 are analyzed to determine femur referencedata [block 110]. For example, the coronal 2D images are analyzed todetermine the most distal femur point D₁ on a healthy condyle and ajoint line perpendicular to a trochlear groove line is used to estimatethe location of a hypothetical most distal point D₂ on the damagedcondyle. Similarly, the axial 2D images are analyzed to determine themost posterior femur point P₁ on a healthy condyle and a joint lineperpendicular to a trochlear groove line is used to estimate thelocation of a hypothetical most posterior point P₂ on the damagedcondyle. The femur reference data points D₁, D₂, P₁, P₂ is mapped orotherwise imported to a sagittal or y-z plane in a computer environmentand used to determine the sagittal or y-z plane relationship between thefemur reference data points D₁, D₂, P₁, P₂. The femur reference data D₁,D₂, P₁, P₂ is then used to choose candidate femoral implant(s). [Block112]. The femur reference data points D₁, D₂, P₁, P₂ are respectivelycorrelated with similar reference data points D₁′, D₂′, P₁′, P₂′ of theselected femur implant 34 in a sagittal or y-z plane [block 114]. Thiscorrelation determines the locations and orientations of the cut plane30 and drill holes 32 needed to cause the patient's joint to returned toa natural, pre-deteriorated alignment with the selected implant 34. Thecut plane 30 and drill hole 32 locations determined in block 114 areadjusted to account for cartilage thickness [block 118].

As shown in FIG. 1C2 at block 120, tibia reference data is determinedfrom the images in a manner similar to the process of block 110, exceptdifferent image planes are employed. Specifically, sagittal and coronalimages slices of the tibia are analyzed to identify the lowest (i.e.,most distal) and most anterior and posterior points of the tibiarecessed condylar surfaces. This tibia reference data is then projectedonto an axial view. The tibia reference data is used to select anappropriate tibia implant [Block 121]. The tibia reference data iscorrelated to similar reference data of the selected tibia implant in amanner similar to that of block 114, except the correlation takes placein an axial view [Block 122]. The cut plane 30 associated with the tibiaimplant's position determined according to block 122 is adjusted toaccount for cartilage thickness [Block 123].

Once the saw cut locations 30 and drill hole locations 32 associatedwith the POP of the femur and tibia implants 34 has been completed withrespect to the femur and tibia data 28 (e.g., the 2D femur and tibiaimages 16 and reference point W), the saw cut locations 30 and drillhole locations 32 are packaged relative to the reference pointW(X_(0-j), Y_(0-j), Z_(0-j)) [Block 124]. As the images 16 and otherdata created from the images or by employing the images may have movedduring any of the processes discussed in blocks 110-123, the referencepoint W(X_(0-j), Y_(0-j), Z_(0-j)) for the images or associated data maybecome updated reference point W′ at coordinates (X_(0-k), Y_(0-k),Z_(0-k)) relative to an origin (X₀, Y₀, Z₀) of an X-Y-Z axis. Forexample, during the correlation process discussed in blocks 114 and 122,the implant reference data may be moved towards the bone image referencedata or, alternatively, the bone image reference data may be movedtowards the implant reference data. In the latter case, the location ofthe bone reference data will move from reference point W(X_(0-j),Y_(0-j), Z_(0-j)) to updated reference point W′(X_(0-k), Y_(0-k),Z_(0-k)), and this change in location with respect to the origin willneed to be matched by the arthritic models 36 to allow for “saw cut anddrill hole” data 44 obtained via the POP process of blocks 110-125 to bemerged with “jig data” 46 obtained via the jig mating surface definingprocess of blocks 130-145, as discussed below.

As can be understood from FIG. 1E, the POP process may be completed withthe packaging of the saw cut locations 30 and drill hole locations 32with respect to the updated reference point W′(X_(0-k), Y_(0-k),Z_(0-k)) as “saw cut and drill hole data” 44 [Block 125]. The “saw cutand drill hole data” 44 is then used as discussed below with respect to[block 150] in FIG. 1E.

In one embodiment, the POP procedure is a manual process, wherein 2Dbone images 28 (e.g., femur and tibia 2D images in the context of thejoint being a knee) are manually analyzed to determine reference data toaid in the selection of a respective implant 34 and to determine theproper placement and orientation of saw cuts and drill holes that willallow the selected implant to restore the patient's joint to its naturalpre-deteriorated state. (The reference data for the 2D bone images 28may be manually calculated or calculated by a computer by a personsitting in front of a computer 6 and visually observing the images 28 onthe computer screen 9 and determining the reference data via thecomputer controls 11. The data may then be stored and utilized todetermine the candidate implants and proper location and orientation ofthe saw cuts and drill holes. In other embodiments, the POP procedure istotally computer automated or a combination of computer automation andmanual operation via a person sitting in front of the computer.

In some embodiments, once the selection and placement of the implant hasbeen achieved via the 2D POP processes described in blocks 110-125, theimplant selection and placement may be verified in 2D by superimposingthe implant models 34 over the bone images data, or vice versa.Alternatively, once the selection and placement of the implant has beenachieved via the 2D POP processes described in blocks 110-125, theimplant selection and placement may be verified in 3D by superimposingthe implant models 34 over 3D bone models generated from the images 16.Such bone models may be representative of how the respective bones mayhave appeared prior to degeneration. In superimposing the implants andbones, the joint surfaces of the implant models can be aligned or causedto correspond with the joint surfaces of the 3D bone models. This endsthe overview of the POP process. A more detailed discussion of variousembodiments of the POP process is provided later in this DetailedDescription

As can be understood from FIG. 1D, the 2D images 16 employed in the 2DPOP analysis of blocks 110-124 of FIGS. 1C1-1C2 are also used to createcomputer generated 3D bone and cartilage models (i.e., “arthriticmodels”) 36 of the bones 18, 20 forming the patient's joint 14 [block130]. Like the above-discussed 2D images and femur and tibia referencedata, the arthritic models 36 are located such that point W is atcoordinates (X_(0-j), Y_(0-j), Z_(0-j)) relative to the origin (X₀, Y₀,Z₀) of the X-Y-Z axis [block 130]. Thus, the 2D images and femur andtibia data of blocks 110-125 and arthritic models 36 share the samelocation and orientation relative to the origin (X₀, Y₀, Z₀). Thisposition/orientation relationship is generally maintained throughout theprocess discussed with respect to FIGS. 11B-1E. Accordingly, movementsrelative to the origin (X₀, Y₀, Z₀) of the 2D images and femur and tibiadata of blocks 110-125 and the various descendants thereof (i.e., bonecut locations 30 and drill hole locations 32) are also applied to thearthritic models 36 and the various descendants thereof (i.e., the jigmodels 38). Maintaining the position/orientation relationship betweenthe 2D images and femur and tibia data of blocks 110-125 and arthriticmodels 36 and their respective descendants allows the “saw cut and drillhole data” 44 to be integrated into the “jig data” 46 to form the“integrated jig data” 48 employed by the CNC machine 10 to manufacturethe customized arthroplasty jigs 2, as discussed with respect to block150 of FIG. 1E.

Computer programs for creating the 3D computer generated arthriticmodels 36 from the 2D images 16 include: Analyze from AnalyzeDirect,Inc., Overland Park, Kans.; Insight Toolkit, an open-source softwareavailable from the National Library of Medicine Insight Segmentation andRegistration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-sourcesoftware available from www.slicer.org: Mimics from Materialise, AnnArbor. Mich.: and Paraview available at www.paraview.org.

The arthritic models 36 depict the bones 18, 20 in the presentdeteriorated condition with their respective degenerated joint surfaces24, 26, which may be a result of osteoarthritis, injury, a combinationthereof, etc. The arthritic models 36 also include cartilage in additionto bone. Accordingly, the arthritic models 36 depict the arthroplastytarget areas 42 generally as they will exist when the customizedarthroplasty jigs 2 matingly receive the arthroplasty target areas 42during the arthroplasty surgical procedure.

As indicated in FIG. 1D and already mentioned above, to coordinate thepositions/orientations of the 2D images and femur and tibia data ofblocks 110-125 and arthritic models 36 and their respective descendants,any movement of the 2D images and femur and tibia data of blocks 110-125from point W to point W′ is tracked to cause a generally identicaldisplacement for the “arthritic models” 36, and vice versa [block 135].

As depicted in FIG. 1D, computer generated 3D surface models 40 of thearthroplasty target areas 42 of the arthritic models 36 are importedinto computer generated 3D arthroplasty jig models 38 [block 140]. Thus,the jig models 38 are configured or indexed to matingly receive thearthroplasty target areas 42 of the arthritic models 36. Jigs 2manufactured to match such jig models 38 will then matingly receive thearthroplasty target areas of the actual joint bones during thearthroplasty surgical procedure.

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is a manual process. The 3D computergenerated models 36, 38 are manually manipulated relative to each otherby a person sitting in front of a computer 6 and visually observing thejig models 38 and arthritic models 36 on the computer screen 9 andmanipulating the models 36, 38 by interacting with the computer controls11. In one embodiment, by superimposing the jig models 38 (e.g., femurand tibia arthroplasty jigs in the context of the joint being a knee)over the arthroplasty target areas 42 of the arthritic models 36, orvice versa, the surface models 40 of the arthroplasty target areas 42can be imported into the jig models 38, resulting in jig models 38indexed to matingly receive the arthroplasty target areas 42 of thearthritic models 36. Point W′ (X_(0-k), Y_(0-k), Z_(0-k)) can also beimported into the jig models 38, resulting in jig models 38 positionedand oriented relative to point W′ (X_(0-k), Y_(0-k), Z_(0-k)) to allowtheir integration with the bone cut and drill hole data 44 of [block125].

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is generally or completely automated, asdisclosed in U.S. patent application Ser. No. 11/959,344 to Park, whichis entitled System and Method for Manufacturing Arthroplasty Jigs, wasfiled Dec. 18, 2007, now U.S. Pat. No. 8,221,430 and is incorporated byreference in its entirety into this Detailed Description. For example, acomputer program may create 3D computer generated surface models 40 ofthe arthroplasty target areas 42 of the arthritic models 36. Thecomputer program may then import the surface models 40 and point W′(X_(0-k), Y_(0-k), Z_(0-k)) into the jig models 38, resulting in the jigmodels 38 being indexed to matingly receive the arthroplasty targetareas 42 of the arthritic models 36. The resulting jig models 38 arealso positioned and oriented relative to point W′ (X_(0-k), Y_(0-k),Z_(0-k)) to allow their integration with the bone cut and drill holedata 44 of [block 125].

In one embodiment, the arthritic models 36 may be 3D volumetric modelsas generated from the closed-loop process discussed in U.S. patentapplication Ser. No. 11/959,344 filed by Park. In other embodiments, thearthritic models 36 may be 3D surface models as generated from theopen-loop process discussed in U.S. patent application Ser. No.11/959,344 filed by Park.

In one embodiment, the models 40 of the arthroplasty target areas 42 ofthe arthritic models 36 may be generated via an overestimation processas disclosed in U.S. Provisional Patent Application 61/083,053, which isentitled System and Method for Manufacturing Arthroplasty Jigs HavingImproved Mating Accuracy, was filed by Park Jul. 23, 2008, and is herebyincorporated by reference in its entirety into this DetailedDescription.

As indicated in FIG. 1E, in one embodiment, the data regarding the jigmodels 38 and surface models 40 relative to point W′ (X_(0-k), Y_(0-k),Z_(0-k)) is packaged or consolidated as the “jig data” 46 [block 145].The “jig data” 46 is then used as discussed below with respect to [block150] in FIG. 1E.

As can be understood from FIG. 1E, the “saw cut and drill hole data” 44is integrated with the “jig data” 46 to result in the “integrated jigdata” 48 block 1501. As explained above, since the “saw cut and drillhole data” 44, “jig data” 46 and their various ancestors (e.g., 2Dimages and femur and tibia data of blocks 110-125 and models 36, 38) arematched to each other for position and orientation relative to point Wand W′, the “saw cut and drill hole data” 44 is properly positioned andoriented relative to the “jig data” 46 for proper integration into the“jig data” 46. The resulting “integrated jig data” 48, when provided tothe CNC machine 10, results in jigs 2: (1) configured to matinglyreceive the arthroplasty target areas of the patient's bones; and (2)having cut slots and drill holes that facilitate preparing thearthroplasty target areas in a manner that allows the arthroplasty jointimplants to generally restore the patient's joint line to itspre-degenerated state or natural alignment state.

As can be understood from FIGS. 1A and 1E, the “integrated jig data” 44is transferred from the computer 6 to the CNC machine 10 [block 155].Jig blanks 50 are provided to the CNC machine 10 [block 160], and theCNC machine 10 employs the “integrated jig data” to machine thearthroplasty jigs 2 from the jig blanks 50 [block 165].

For a discussion of example customized arthroplasty cutting jigs 2capable of being manufactured via the above-discussed process, referenceis made to FIGS. 2A-2D. While, as pointed out above, the above-discussedprocess may be employed to manufacture jigs 2 configured forarthroplasty procedures involving knees, elbows, ankles, wrists, hips,shoulders, vertebra interfaces, etc., the jig examples depicted in FIGS.2A-2D are for total knee replacement (“TKR”) or partial knee(“uni-knee”) replacement procedures. Thus, FIGS. 2A and 2B are,respectively, bottom and top perspective views of an example customizedarthroplasty femur jig 2A, and FIGS. 2C and 2D are, respectively, bottomand top perspective views of an example customized arthroplasty tibiajig 2B.

As indicated in FIGS. 2A and 2B, a femur arthroplasty jig 2A may includean interior side or portion 98 and an exterior side or portion 102. Whenthe femur cutting jig 2A is used in a TKR procedure, the interior sideor portion 98 faces and matingly receives the arthroplasty target area42 of the femur lower end, and the exterior side or portion 102 is onthe opposite side of the femur cutting jig 2A from the interior portion98.

The interior portion 98 of the femur jig 2A is configured to match thesurface features of the damaged lower end (i.e., the arthroplasty targetarea 42) of the patient's femur 18. Thus, when the target area 42 isreceived in the interior portion 98 of the femur jig 2A during the TKRsurgery, the surfaces of the target area 42 and the interior portion 98match.

The surface of the interior portion 98 of the femur cutting jig 2A ismachined or otherwise formed into a selected femur jig blank 50A and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged lower end or target area 42 of the patient's femur 18.

As indicated in FIGS. 2C and 2D, a tibia arthroplasty jig 2B may includean interior side or portion 104 and an exterior side or portion 106.When the tibia cutting jig 2B is used in a TKR procedure, the interiorside or portion 104 faces and matingly receives the arthroplasty targetarea 42 of the tibia upper end, and the exterior side or portion 106 ison the opposite side of the tibia cutting jig 2B from the interiorportion 104.

The interior portion 104 of the tibia jig 2B is configured to match thesurface features of the damaged upper end (i.e., the arthroplasty targetarea 42) of the patient's tibia 20. Thus, when the target area 42 isreceived in the interior portion 104 of the tibia jig 2B during the TKRsurgery, the surfaces of the target area 42 and the interior portion 104match.

The surface of the interior portion 104 of the tibia cutting jig 2B ismachined or otherwise formed into a selected tibia jig blank 50B and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged upper end or target area 42 of the patient's tibia 20.

While the discussion provided herein is given in the context of TKR andTKR jigs and the generation thereof, the disclosure provided herein isreadily applicable to uni-compartmental or partial arthroplastyprocedures in the knee or other joint contexts. Thus, the disclosureprovided herein should be considered as encompassing jigs and thegeneration thereof for both total and uni-compartmental arthroplastyprocedures.

The remainder of this Detailed Discussion will now focus on variousembodiments for performing POP.

B. Overview of Preoperative Planning (“POP”) Procedure

In one embodiment, as can be understood from [blocks 100-110] of FIGS.1B-1C2, medical images 16 of the femur and tibia 18, 20 are generated[Blocks 100 and 105] and coronal, axial and sagittal image slices areanalyzed to determine reference data 28, 100, 900. [Block 115]. Thesizes of the implant models 34 are selected relative to the femur andtibia reference data. [Block 112, 114 and 121, 122]. The reference data28, 100, 900 is utilized with the data associated with implant models 34to determine the cut plane location. The joint spacing between the femurand the tibia is determined. An adjustment value tr is determined toaccount for cartilage thickness or joint gap of a restored joint. Theimplant models 34 are shifted or adjusted according to the adjustmentvalue tr [blocks 118 and 123]. Two dimensional computer implant models34 are rendered into the two dimensional imaging slice(s) of the bones28 such that the 2D implant models 34 appear alongside the 2D imagingslices of the bones 28. In one embodiment, ITK software, manufactured byKitware, Inc. of Clifton Park. N.Y. is used to perform this rendering.Once the 2D implant models 34 are rendered into the MRI/CT image, theproper selection, orientation and position of the implant models can beverified. An additional verification process may be used wherein 3Dmodels of the bones and implants are created and proper positioning ofthe implant may be verified. Two dimensional computer models 34 andthree dimensional computer models 1004, 1006 of the femur and tibiaimplants are generated from engineering drawings of the implants and maybe generated via any of the above-referenced 2D and 3D modeling programsto confirm planning. If the implant sizing is not correct, then theplanning will be amended by further analysis of the 2D images. If theimplant sizing is accurate, then planning is complete. The process thencontinues as indicated in [block 125] of FIG. 11E.

This ends the overview of the POP process. The following discussionswill address each of the aspects of the POP process in detail.

C. Femur and Tibia Images

FIG. 3A depicts 2D bone models or images 28′, 28″ of the femur and tibia18, 20 from medical imaging scans 16. While FIG. 3A represents thepatient's femur 18 and tibia 20 prior to injury or degeneration, it canbe understood that, in other embodiments, the images 28′, 28″ may alsorepresent the patient's femur 18 and tibia 20 after injury ordegeneration. More specifically. FIG. 3A is a 2D image slice 28′ of afemur lower end 200 and an 2D image slice 28″ of a tibia upper end 205representative of the corresponding patient bones 18, 20 in anon-deteriorated state and in position relative to each to form a kneejoint 14. The femur lower end 200 includes condyles 215, and the tibiaupper end 205 includes a plateau 220. The images or models 28′, 28″ arepositioned relative to each other such that the curved articularsurfaces of the condyles 215, which would normally mate withcomplementary articular surfaces of the plateau 220, are instead notmating, but roughly positioned relative to each other to generallyapproximate the knee joint 14.

As generally discussed above with respect to FIGS. 1A-1C2, the POPbegins by using a medical imaging process, such as magnetic resonanceimaging (MRI), computed tomography (CT), and/or another other medicalimaging process, to generate imaging data of the patient's knee. Forexample, current commercially available MRI machines use 8 bit (255grayscale) to show the human anatomy. Therefore, certain components ofthe knee, such as the cartilage, cortical bone, cancellous bone,meniscus, etc., can be uniquely viewed and recognized with 255grayscale. The generated imaging data is sent to a preoperative planningcomputer program. Upon receipt of the data, a user or the computerprogram may analyze the data (e.g., two-dimensional MRI images 16, andmore specifically, the 2D femur image(s) 28′ or 2D tibia image(s) 28″)to determine various reference points, reference lines and referenceplanes. In one embodiment, the MRI imaging scans 16 may be analyzed andthe reference data for POP may be generated by a proprietary softwareprogram called PerForm.

For greater detail regarding the methods and systems for computermodeling joint bones, such as the femur and tibia bones forming theknee, please see the following U.S. patent applications, which are allincorporated herein in their entireties: U.S. patent application Ser.No. 11/656,323 to Park et al., titled “Arthroplasty Devices and RelatedMethods” and filed Jan. 19, 2007, now U.S. Pat. No. 9,017,336; U.S.patent application Ser. No. 10/146,862 to Park et al., titled “ImprovedTotal Joint Arthroplasty System” and filed May 15, 2002; U.S. patentSer. No. 11/642,385 to Park et al., titled “Arthroplasty Devices andRelated Methods” and filed Dec. 19, 2006.

FIG. 3B is an isometric view of a computer model of a femur implant 34′and a computer model of a tibia implant 34″ in position relative to eachto form an artificial knee joint 14. The computer models 34′, 34″ may beformed, for example, via computer aided drafting or 3D modelingprograms. As will be discussed later in this detailed description, theimplant computer models may be in 2D or in 3D as necessary for theparticular planning step.

The femur implant model 34′ will have a joint side 240 and a boneengaging side 245. The joint side 240 will have a condyle-like surfacefor engaging a complementary surface of the tibia implant model 34″. Thehone engaging side 245 will have surfaces and engagement features 250for engaging the prepared (i.e., sawed to shape) lower end of the femur18.

The tibia implant model 34″ will have a joint side 255 and a boneengaging side 260. The joint side 255 will have a plateau-like surfaceconfigured to engage the condyle-like surface of the femur implant model34′. The bone engaging side 260 will have an engagement feature 265 forengaging the prepared (i.e., sawed to shape) upper end of the tibia 20.

As discussed in the next subsections of this Detailed Description, thereference data of the femur and tibia bone models or images 28′, 28″ maybe used in conjunction with the implant models 34′, 34″ to select theappropriate sizing for the implants actually to be used for the patient.The resulting selections can then be used for planning purposes, asdescribed later in this Detailed Description.

D. Femur Planning Process

For a discussion of the femur planning process, reference is now made toFIGS. 4-22. FIGS. 4-9 illustrate a process in the POP wherein the system4 utilizes 2D imaging slices (e.g., MRI slices, CT slices, etc.) todetermine femur reference data, such as reference points, lines andplanes via their relationship to the trochlear groove plane-GHO of thefemur. The resulting femur reference data 100 is then mapped orprojected to a y-z coordinate system (sagittal plane). The femurreference data is then applied to a candidate femur implant model,resulting in femoral implant reference data 100′. The data 100, 100′ isutilized to select an appropriate set of candidate implants, from whicha single candidate implant will be chosen, which selection will bediscussed in more detail below with reference to FIGS. 10-22.

1, Determining Femur Reference Data

For a discussion of a process used to determine the femur referencedata, reference is now made to FIGS. 4-7C. FIG. 4 is a perspective viewof the distal end of a 3D model 1000 of the femur image of FIG. 3Awherein the femur reference data 100 is shown. As will be explained inmore detail below, the femur reference data is generated by an analysisof the 2D image scans and FIG. 4 depicts the relative positioning of thereference data on a 3D model. As shown in FIG. 4, the femur referencedata 100 may include reference points (e.g. D₁, D₂), reference lines(e.g. GO, EF) and reference planes (e.g. P, S). The femur reference data100 may be determined by a process illustrated in FIGS. 5A-7D anddescribed in the next sections.

As shown in FIG. 5A, which is a sagittal view of a femur 18 illustratingthe orders and orientations of imaging slices 16 that are utilized inthe femur POP, a multitude of image slices may be compiled. In someembodiments, the image slices may be analyzed to determine, for example,distal contact points prior to or instead of being compiled into a bonemodel. Image slices may extend medial-lateral in planes that would benormal to the longitudinal axis of the femur, such as image slices 1-5of FIGS. 5A and 6D. Image slices may extend medial-lateral in planesthat would be parallel to the longitudinal axis of the femur, such asimage slices 6-9 of FIGS. 5A and 7B. The number of image slices may varyfrom 1-50 and may be spaced apart in a 2 mm spacing or other spacing.

a. Determining Reference Points P₁P₂

In some embodiments, the planning process begins with the analysis ofthe femur slices in a 2D axial view. As can be understood from FIG. 5B,which depicts axial imaging slices of FIG. 5A, the series of 2D axialfemur slices are aligned to find the most posterior point of eachcondyle. For example, the most posterior points of slice 5, P_(1A),P_(2A), are compared to the most posterior points of slice 4, P_(1B),P_(2B). The most posterior points of slice 4 are more posterior thanthose of slice 5. Therefore, the points of slice 4 will be compared toslice 3. The most posterior points of slice 3, P_(1C), P_(2C), are moreposterior than the posterior points P_(1B), P_(2B) of slice 4.Therefore, the points of slice 3 will be compared to slice 2. The mostposterior points of slice 2, P_(1D), P_(2D), are more posterior than theposterior points P_(1C), P_(2C) of slice 3. Therefore, the points ofslice 2 will be compared to slice 1. The most posterior points of slice1, P_(1E), P_(2E), are more posterior than the posterior points P_(1D),P_(2D) of slice 2. In some embodiments, the points of slice 1 may becompared to slice 0 (not shown). The most posterior points of slice 0,P_(1F), P_(F), are less posterior than the posterior points P_(1E),P_(2E) of slice 1. Therefore, the points of slice 1 are determined to bethe most posterior points P₁P₂ of the femur. In some embodiments, pointsP₁ and P₂ may be found on different axial slices. That is, the mostposterior point on the medial side and most posterior point on thelateral side may lie in different axial slices. For example, slice 2 mayinclude the most posterior point on the lateral side, while slice 1 mayinclude the most posterior point on the medial side. It can beappreciated that the number of slices that are analyzed as describedabove may be greater than five slices or less than five slices. Thepoints P₁, P₂ are stored for later analysis.

b. Determining Reference Points D₁, D₂

The planning process continues with the analysis of the femur slices ina 2D coronal view. As can be understood from FIG. 5C, which depictscoronal imaging slices of FIG. 5A, the series of 2D coronal femur slicesare aligned to find the most distal point of each condyle. For example,the most distal points of slice 6, D_(1A), D_(2A), are compared to themost distal points of slice 7, D_(1B), D_(2B). The most distal points ofslice 7 are more distal than those of slice 6. Therefore, the points ofslice 7 will be compared to slice 8. The most distal points of slice 8,D_(1C), D_(2C), are more distal than the distal points D_(1B), D_(2B) ofslice 7. Therefore, the points of slice 8 will be compared to slice 9.The most distal points of slice 9, D_(1D), D_(2D), are more distal thanthe distal points D_(1C), D_(2C) of slice 8. In some embodiments, thepoints of slice 9 may be compared to slice 10 (not shown). The mostdistal points of slice 10, D_(1E), D_(2E), are less distal than thedistal points D_(1D), D_(2D) of slice 9. Therefore, the points of slice9 are determined to be the most distal points D₁, D₂ of the femur. Insome embodiments, points D₁ and D₂ may be found on different coronalslices. That is, the most distal point on the medial side and mostdistal point on the lateral side may lie in different coronal slices.For example, slice 9 may include the most distal point on the lateralside, while slice 8 may include the most distal point on the medialside. It can be appreciated that the number of slices that are analyzedas described above may be greater than four slices or less than fourslices. The points D₁, D₂ are stored for future analysis.

c. Determining Reference Lines CD and GO

Analysis of the 2D slices in the axial view aid in the determination ofinternal/external rotation adjustment. The points D₁, D₂ represent thelowest contact points of each of the femoral lateral and medial condyles302, 303. Thus, to establish an axial-distal reference line, line CD, in2D image slice(s), the analysis utilizes the most distal point, eitherD₁ or D₂, from the undamaged femoral condyle. For example, as shown inFIG. 6A, which is an axial imaging slice of the femur of FIG. 5A, whenthe lateral condyle 302 is undamaged but the medial condyle 303 isdamaged, the most distal point D₁ will be chosen as the reference pointin establishing the axial-distal reference line, line CD. The line CD isextended from the lateral edge of the lateral condyle, through point D₁,to the medial edge of the medial condyle. If the medial condyle wasundamaged, then the distal point D₂ would be used as the reference pointthrough which line CD would be extended. The distal points D₁, D₂ andline CD are stored for later analysis.

A line CD is verified. A most distal slice of the series of axial viewsis chosen to verify the position of an axial-distal reference line, lineCD. As shown in FIG. 6A, the most distal slice 300 of the femur (e.g.,slice 5 in FIGS. 5A and 6D) is chosen to position line CD such that lineCD is generally anteriorly-posteriorly centered in the lateral andmedial condyles 302, 303. Line CD is generally aligned with the corticalbone of the undamaged posterior condyle. For example, if the medialcondyle 303 is damaged, the line CD will be aligned with the undamagedlateral condyle, and vice versa. To verify the location of line CD andas can be understood from FIGS. 4 and 6C, the line CD will also connectthe most distal points D₁, D₂. The geography information of line CD willbe stored for future analysis.

Line GO is determined. The “trochlear groove axis” or the “trochleargroove reference plane” is found. In the knee flexion/extension motionmovement, the patella 304 generally moves up and down in the femoraltrochlear groove along the vertical ridge and generates quadricepsforces on the tibia. The patellofemoral joint and the movement of thefemoral condyles play a major role in the primary structure andmechanics across the joint. In a normal knee model or properly alignedknee, the vertical ridge of the posterior patella is generally straight(vertical) in the sliding motion. For the OA patients' knees, there israrely bone damage in the trochlear groove: there is typically onlycartilage damage. Therefore, the trochlear groove of the distal femurcan serve as a reliable bone axis reference. In relation to the jointline assessment, as discussed with reference to FIGS. 14A-14J, thetrochlear groove axis of the distal femur is perpendicular or nearlyperpendicular to the joint line of the knee. A detailed discussion ofthe trochlear groove axis or the trochlear groove reference plane may befound in co-owned U.S. patent application Ser. No. 12/111,924, now U.S.Pat. No. 8,480,679, which is incorporated by reference in its entirety.

To perform the trochlear groove analysis, the MRI slice in the axialview with the most distinct femoral condyles (e.g., the slice with thelargest condyles such as slice 400 of FIG. 6B) will be chosen toposition the trochlear groove bisector line, line TGB. As shown in FIG.6B, which is an axial imaging slice of the femur of FIG. 5A, the mostdistinct femoral condyles 302, 303 are identified. The trochlear groove405 is identified from image slice 400. The lowest extremity 406 of thetrochlear groove 405 is then identified. Line TGB is then generallyaligned with the trochlear groove 405 across the lowest extremity 406.In addition, and as shown in FIG. 6D, which is the axial imaging slices1-5 taken along section lines 1-5 of the femur in FIG. 5A, each of theslices 1-5 can be aligned vertically along the trochlear groove 405,wherein points G1, G2, G3, G4, G5 respectively represent the lowestextremity 406 of trochlear groove 405 for each slice 1-5. By connectingthe various points G1, G2, G3, G4, G5, a point O can be obtained. As canbe understood from FIGS. 4 and 6C, resulting line GO is perpendicular ornearly perpendicular to line D₁ D₂. In a 90° knee extension, line GO isperpendicular or nearly perpendicular to the joint line of the knee andline P₁P₂. Line GO is stored for later analysis.

d. Determining Reference Lines EF and HO

Analysis of the 2D slices in the coronal view aid in the determinationof femoral varus/valgus adjustment. The points P₁, P₂ determined aboverepresent the most posterior contact points of each of the femorallateral and medial condyles 302, 303. Thus, to establish a coronalposterior reference line, line EF, in 2D image slice(s), the analysisutilizes the most posterior point, either P₁ or P₂, from the undamagedfemoral condyle. For example, as shown in FIG. 7A, when the lateralcondyle 302 is undamaged but the medial condyle 303 is damaged, the mostposterior point P₁ will be chosen as the reference point in establishingthe coronal posterior reference line, line EF. The line EF is extendedfrom the lateral edge of the lateral condyle, through point P₁, to themedial edge of the medial condyle. If the medial condyle was undamaged,then the posterior point P₂ would be used as the reference point throughwhich line EF would be extended. The posterior points P₁, P₂ and line EFare stored for later analysis.

The points, P₁P₂ were determined as described above with reference toFIG. 5B. Line EF is then verified. A most posterior slice of the seriesof coronal views is chosen to verify the position of a coronal posteriorreference line, line EF. As shown in FIG. 7A, which is a coronal imagingslice of FIG. 5A, the most posterior slice 401 of the femur (e.g., slice6 in FIGS. 5A and 7B) is chosen to position line EF such that line EF isgenerally positioned in the center of the lateral and medial condyles302, 303. Line EF is generally aligned with the cortical bone of theundamaged posterior condyle. For example, if the medial condyle 303 isdamaged, the line EF will be aligned with the undamaged lateral condyle,and vice versa. To verify the location of line EF and as can beunderstood from FIG. 4, the line EF will also connect the most posteriorpoints P₁, P₂. The geography information of line EF will be stored forfuture analysis.

In some embodiments, line HO may be determined. As shown in FIG. 7B,which are coronal imaging slices 6-9 taken along section lines 6-9 ofthe femur in FIG. 5A, each of the image slices 6-9 taken from FIG. 5Acan be aligned along the trochlear groove. The points H6, H7, H8, H9respectively represent the lowest extremity of the trochlear groove foreach of the image slices 6-8 from FIG. 5A. By connecting the variouspoints H6. H7. H8, the point O can again be obtained. The resulting lineHO is established as the shaft reference line-line SHR. Thecoronal-posterior reference line, line EF and coronal-distal referenceline, line AB may be adjusted to be perpendicular or nearlyperpendicular to the shaft reference line-line SHR (line HO). Thus, theshaft reference line, line SHR (line HO) is perpendicular or nearlyperpendicular to the coronal-posterior reference line, line EF and tothe coronal-distal reference line, line AB throughout the coronal imageslices.

As can be understood from FIGS. 4 and 7B, the trochlear grooveplane-GHO, as the reference across the most distal extremity of thetrochlear groove of the femur and in a 90° knee extension, should beperpendicular to line AB. The line-HO, as the reference across the mostposterior extremity of trochlear groove of the femur and in a 0° kneeextension, should be perpendicular to line AB.

e. Determining Reference Line AB and Reference Planes P and S

As can be understood from FIG. 4, a posterior plane S may be constructedsuch that the plane S is normal to line GO and includes posteriorreference points P₁, P₂. A distal plane P may be constructed such thatit is perpendicular to posterior plane S and may include distalreference points D₁, D₂ (line CD). Plane P is perpendicular to plane Sand forms line AB therewith. Line HO and line GO are perpendicular ornearly perpendicular to each other. Lines CD, AB and EF are parallel ornearly parallel to each other. Lines CD. AB and EF are perpendicular ornearly perpendicular to lines HO and GO and the trochlear plane GHO.

f. Verification of the Femoral Reference Data

As shown in FIG. 7C, which is an imaging slice of the femur of FIG. 5Ain the sagittal view, after the establishment of the reference linesfrom the axial and coronal views, the axial-distal reference line CD andcoronal-posterior reference line EF and planes P, S are verified in the2D sagittal view. The sagittal views provide the extension/flexionadjustment. Thus, as shown in FIG. 7C, slice 800 shows a sagittal viewof the femoral medial condyle 303. Line-bf and line-bd intersect atpoint-b. As can be understood from FIGS. 4 and 7C, line-bf falls on thecoronal plane-S, and line-bd falls on the axial plane-P. Thus, in oneembodiment of POP planning, axial and coronal views are used to generateaxial-distal and coronal-posterior reference lines CD, EF. These tworeference lines CD, EF can be adjusted (via manipulation of thereference data once it has been imported and opened on the computer) totouch in the black cortical rim of the femur. The adjustment of the tworeference lines on the femur can also be viewed simultaneously in thesagittal view of the MRI slice, as displayed in FIG. 7C. Thus, thesagittal view in FIG. 7C provides one approach to verify if the tworeference lines do touch or approximately touch with the femur corticalbone. In some embodiments, line-bf is perpendicular or nearlyperpendicular to line-bd. In other embodiments, line bf may not beperpendicular to bd. This angle depends at least partially on therotation of femoral bone within MRI.

With reference to FIGS. 4-7C, in one embodiment, lines HO and GO may bewithin approximately six degrees of being perpendicular with lines P₁P₂,D₁D₂ and A₁A₂ or the preoperative planning for the distal femur will berejected and the above-described processes to establish the femoralreference data 100 (e.g. reference lines CD, EF, AB, reference pointsP₁P₂, D₁D₂) will be repeated until the femoral reference data meets thestated tolerances, or a manual segmentation for setting up the referencelines will be performed. In other embodiments, if there are multiplefailed attempts to provide the reference lines, then the reference datamay be obtained from another similar joint that is sufficiently free ofdeterioration. For example, in the context of knees, if repeatedattempts have been made without success to determined reference data ina right knee medial femur condyle based on data obtained from the rightknee lateral side, then reference data could be obtained from the leftknee lateral or medial sides for use in the determination of the femoralreference data.

g. Mapping the Femoral Reference Data to a Y-Z Plane

As can be understood from FIGS. 7D-9, the femoral reference data 100will be mapped to a y-z coordinate system to aid in the selection of anappropriate implant. As shown in FIGS. 7D-7E, which are axial andcoronal slices, respectively, of the femur, the points D₁D₂ of thedistal reference line D₁D₂ or CD were determined from both a 2D axialview and a 2D coronal view and therefore are completely defined in 3D.Similarly, the points P₁P₂ of the posterior reference line P₁P₂ or EFwere determined from both a 2D axial view and a 2D coronal view andtherefore are completely defined in 3D.

As shown in FIG. 8, which is a posterior view of a femur 3D model 1000,the reference data 100 determined by an analysis of 2D images may beimported onto a 3D model of the femur for verification purposes. Thedistance L between line EF and line CD can be determined and stored forlater analysis during the selection of an appropriate implant size.

As indicated in FIG. 9, which depicts a y-z coordinate system, theposterior points P₁P₂ and distal points D₁D₂ of the 2D images 28′ mayalso be projected onto a y-z plane and this information is stored forlater analysis.

2. Determining Femoral Implant Reference Data

There are 6 degrees of freedom for a femoral implant to be moved androtated for placement on the femoral bone. The femur reference data 100(e.g. points P₁P₂, D₁D₂, reference lines EF, CD, reference planes P, S)is utilized in the selection and placement of the femoral implant. For adiscussion of a process used to determine the implant reference data,reference is now made to FIGS. 10-22.

a. Map Femur Reference Data to Implant Model to Establish FemoralImplant Reference Data

As shown in FIGS. 10 and 11, which are perspective views of a femoralimplant model 34′, the femur reference data 100 may be mapped to a 3Dmodel of the femur implant model 34′ in a process of POP. The femurreference data 100 and the femur implant model 34′ are opened together.The femur implant model 34′ is placed on a 3D coordinate system and thedata 100 is also transferred to that coordinate system thereby mappingthe data 100 to the model 34′ to create femoral implant data 100′. Thefemoral implant data 100′ includes an axial-distal reference line(line-C′D′) and a coronal-posterior reference line (line-E′F′).

As can be understood from FIGS. 10 and 11, distal line-D₁′D₂′ representsthe distance between the two most distal points D₁′, D₂′. Posteriorline-P₁′P₂′ represents the distance between the two most posteriorpoints P₁′, P₂′. The lines—D₁′D₂′ P₁′P₂′ of the implant model 34′ can bedetermined and stored for further analysis.

As shown in FIG. 12, which shows a coordinate system wherein some of thefemoral implant reference data 100′ is shown, the endpoints D₁′D₂′ andP₁′P₂′ may also be projected onto a y-z plane and this information isstored for later analysis. As shown in FIG. 13, the implant referencedata 100′ may also be projected onto the coordinate system. The distanceL′ between line E′F′ and line C′D′, and more specifically between linesD₁′D₂′, P₁′P₂′ can be determined and stored for later use during theselection of an implant.

3. Determining Joint Line and Adjustment to Implant that Allows CondylarSurfaces of Implant Model to Restore Joint to Natural Configuration

In order to allow an actual physical arthroplasty implant to restore thepatient's knee to the knee's pre-degenerated or natural configurationwith the natural alignment and natural tensioning in the ligaments, thecondylar surfaces of the actual physical implant generally replicate thecondylar surfaces of the pre-degenerated joint bone. In one embodimentof the systems and methods disclosed herein, condylar surfaces of the 2Dimplant model 34′ are matched to the condylar surfaces of the 2D bonemodel or image 28′. However, because the bone model 28′ may be bone onlyand not reflect the presence of the cartilage that actually extends overthe pre-degenerated condylar surfaces, the alignment of the implant 34′may be adjusted to account for cartilage or proper spacing between thecondylar surfaces of the cooperating actual physical implants (e.g., anactual physical femoral implant and an actual physical tibia implant)used to restore the joint such that the actual physical condylarsurfaces of the actual physical cooperating implants will generallycontact and interact in a manner substantially similar to the way thecartilage covered condylar surfaces of the pre-degenerated femur andtibia contacted and interacted. Thus, in one embodiment, the implantmodels are modified or positionally adjusted to achieve the properspacing between the femur and tibia implants.

a. Determine Adjustment Value tr

To achieve the correct adjustment, an adjustment value tr may bedetermined. In one embodiment, the adjustment value tr may be determinedin 2D by a calipers measuring tool (a tool available as part of thesoftware). The calipers tool is used to measure joint spacing betweenthe femur and the tibia by selection of two points in any of the 2D MRIviews and measuring the actual distance between the points. In anotherembodiment, the adjustment value tr that is used to adjust the implantduring planning may be based off of an analysis associated withcartilage thickness. In another embodiment, the adjustment value tr usedto adjust the implant during planning may be based off of an analysis ofproper joint gap spacing. Both the cartilage thickness and joint gapspacing methods are discussed below in turn.

i. Determining Cartilage Thickness and Joint Line

FIG. 14A shows the femoral condyle 310 and the proximal tibia of theknee in a sagittal MRI image slice. The distal femur 28′ is surroundedby the thin black rim of cortical bone. Due to the nature of irregularbone and cartilage loss in OA patients, it can be difficult to find theproper joint line reference for the models used during the POP.

The space between the elliptical outlining 325′, 325″ along the corticalbone represents the cartilage thickness of the femoral condyle 310. Theellipse contour of the femoral condyle 310 can be seen on the MRI sliceshown in FIG. 14A and obtained by a three-point tangent contact spot(i.e., point t1, t2, t3) method. In a normal, healthy knee, the bonejoint surface is surrounded by a layer of cartilage. Because thecartilage is generally worn-out in OA and the level of cartilage lossvaries from patient to patient, it may be difficult to accuratelyaccount for the cartilage loss in OA patients when trying to restore thejoint via TKA surgery. Therefore, in one embodiment of the methodologyand system disclosed herein, a minimum thickness of cartilage isobtained based on medical imaging scans (e.g., MRI, etc.) of theundamaged condyle. Based on the cartilage information, the joint linereference can be restored. For example, the joint line may be line 630in FIG. 14B.

The system and method disclosed herein provides a POP method tosubstantially restore the joint line back to a “normal or natural knee”status (i.e., the joint line of the knee before OA occurred) andpreserves ligaments in TKA surgery (e.g., for a total knee arthroplastyimplant) or partial knee arthroplasty surgery (e.g., for a uni-kneeimplant).

FIG. 14B is a coronal view of a knee model in extension. As depicted inFIG. 14B, there are essentially four separate ligaments that stabilizethe knee joint, which are the medial collateral ligament (MCL), anteriorcruciate ligament (ACL), lateral collateral ligament (LCL), andposterior cruciate ligament (PCL). The MCL and LCL lie on the sides ofthe joint line and serve as stabilizers for the side-to-side stabilityof the knee joint. The MCL is a broader ligament, whereas the LCL is adistinct cord-like structure.

The ACL is located in the front part of the center of the joint. The ACLis a very important stabilizer of the femur on the tibia and serves toprevent the tibia from rotating and sliding forward during agility,jumping, and deceleration activities. The PCL is located directly behindthe ACL and serves to prevent the tibia from sliding to the rear. Thesystem and method disclosed herein provides POP that allows thepreservation of the existing ligaments without ligament release duringTKA surgery. Also, the POP method provides ligament balance, simplifyingTKA surgery procedures and reducing pain and trauma for OA patients.

As indicated in FIG. 14B, the joint line reference 630 is definedbetween the two femoral condyles 302, 303 and their corresponding tibiaplateau regions 404, 406. Area A illustrates a portion of the lateralfemoral condyle 302 and a portion of the corresponding lateral plateau404 of tibia 205. Area B illustrates the area of interest showing aportion of the medial femoral condyle 303 and a portion of thecorresponding medial plateau 406 of tibia 205.

FIGS. 14C, 14D and 14F illustrate MRI segmentation slices for joint lineassessment. FIG. 14E is a flow chart illustrating the method fordetermining cartilage thickness used to determine proper joint line. Thedistal femur 200 is surrounded by the thin black rim of cortical bone645. The cancellous bone (also called trabecular bone) 650 is an innerspongy structure. An area of cartilage loss 655 can be seen at theposterior distal femur. For OA patients, the degenerative cartilageprocess typically leads to an asymmetric wear pattern that results inone femoral condyle with significantly less articulating cartilage thanthe other femoral condyle. This occurs when one femoral condyle isoverloaded as compared to the other femoral condyle.

As can be understood from FIGS. 14C, 14E and 14F, the minimum cartilagethickness is observed and measured for the undamaged and damaged femoralcondyle 302, 303 [block 1170]. If the greatest cartilage loss isidentified on the surface of medial condyle 303, for example, then thelateral condyle 302 can be used as the cartilage thickness reference forpurposes of POP. Similarly, if the greatest cartilage loss is identifiedon the lateral condyle 302, then the medial condyle 303 can be used asthe cartilage thickness reference for purposes of POP. In other words,use the cartilage thickness measured for the least damaged condylecartilage as the cartilage thickness reference for POP[block 1175].

As indicated in FIG. 14D, the thickness of cartilage can be analyzed inorder to restore the damaged knee compartment hack to its pre-OA status.In each of the MRI slices taken in regions A and B in FIG. 14B, thereference lines as well as the major and minor axes 485, 490 of ellipsecontours 480′, 480″ in one femoral condyle 303 can be obtained.

As shown in FIG. 14F, for the three-point method, the tangents are drawnon the condylar curve at zero degrees and 90 degrees articular contactpoints. The corresponding tangent contact spots t1 and t2 are obtainedfrom the tangents. The line 1450 perpendicular to the line 1455determines the center of the ellipse curve, giving the origin of (0, 0).A third tangent contact spot t3 can be obtained at any point along theellipse contour between the zero degree, t1 point and the 90 degree, t2point. This third spot t3 can be defined as k, where k=1 to n points.

The three-point tangent contact spot analysis may be employed toconfigure the size and radius of the condyle 303 of the femur bone model28′. This provides the “x” coordinate and “y” coordinate, as the (x, y)origin (0, 0) shown in FIG. 14D. The inner ellipse model 480′ of thefemoral condyle shows the femoral condyle surrounded by cortical bonewithout the cartilage attached. The minimum cartilage thickness tm_(min)outside the inner ellipse contour 480′ is measured. Based on theanalysis of the inner ellipse contour 480′ (i.e., the bone surface) andouter ellipse contour 480″ (i.e., the cartilage surface) of the onenon-damaged condyle of the femur bone model 28′, the inner ellipsecontour 480′ (i.e., the bone surface) and the outer ellipse contour 480″(i.e., the cartilage surface) of the other condyle (i.e., the damage ordeteriorated condyle) may be determined.

As can be understood from FIGS. 14B and 14D, ellipse contours 480′, 480″are determined in areas A and B for the condyles 302, 303 of the femurbone model 28′. The inner ellipse contour 480′, representing thebone-only surface, and the outer ellipse contour 480″, representing thebone-and-cartilage surface, can be obtained. The minimum cartilagethickness tm_(min) is measured based on the cartilage thickness trbetween the inner ellipse 480′ and outer ellipse 480″. MRI slices of thetwo condyles 302, 303 of the femur bone model 28′ in areas A and B aretaken to compare the respective ellipse contours in areas A and B. Ifthe cartilage loss is greatest at the medial condyle 303 in the MRIslices, the minimum thickness tm_(min) for the cartilage can be obtainedfrom the lateral condyle 302. Similarly, if the lateral condyle 302 hasthe greatest cartilage loss, the cartilage thickness tm_(min) can beobtained from undamaged medial condyle 303 of the femur restored bonemodel 28′. The minimum cartilage can be illustrated in the formula,tm_(min)=MIN (ti), where i=1 to k.

ii. Determining Joint Gap

As mentioned above, in one embodiment, the adjustment value tr may bedetermined via a joint line gap assessment. The gap assessment may serveas a primary estimation of the gap between the distal femur and proximaltibia of the bone images. The gap assessment may help achieve properligament balancing.

In one embodiment, an appropriate ligament length and joint gap may notbe known from the 2D bone models or images 28′, 28″ (see, e.g. FIG. 3B)as the bone models or images may be oriented relative to each other in afashion that reflects their deteriorated state. For example, as depictedin FIG. 14J, which is a coronal view of bone models 28′, 28″ oriented(e.g., tilted) relative to each other in a deteriorated stateorientation, the lateral side 1487 was the side of the deteriorationand, as a result, has a greater joint gap between the distal femur andthe proximal tibia than the medial side 1485, which was thenon-deteriorated side of the joint in this example.

In one embodiment, ligament balancing may also be considered as a factorfor selecting the appropriate implant size. As can be understood fromFIG. 14J, because of the big joint gap in the lateral side 1487, thepresumed lateral ligament length (L1+L2+L3) may not be reliable todetermine proper ligament balancing. However, the undamaged side, whichin FIG. 14J is the medial side 1485, may be used in some embodiments asthe data reference for a ligament balancing approach. For example, themedial ligament length (M1+M2+M3) of the undamaged medial side 1485 maybe the reference ligament length used for the ligament balancingapproach for implant size selection.

In one embodiment of the implant size selection process, it may beassumed that the non-deteriorated side (i.e., the medial side 1485 inFIG. 14J in this example) may have the correct ligament length forproper ligament balancing, which may be the ligament length of(M1+M2+M3). When the associated ligament length (“ALL”) associated witha selected implant size equals the correct ligament length of(M1+M2+M3), then the correct ligament balance is achieved, and theappropriate implant size has been selected. However, when the ALL endsup being greater than the correct ligament length (M1+M2+M3), theimplant size associated with the ALL may be incorrect and the nextlarger implant size may need to be selected for the design of thearthroplasty jig 2.

For a discussion regarding the gap assessment, which may also be basedon ligament balance off of a non-deteriorated side of the joint,reference is made to FIGS. 14G and 14H. FIGS. 14G and 14H illustratecoronal views of the bone models 28′, 28″ in their post-degenerationalignment relative to each as a result of OA or injury. As shown in FIG.14G, the tibia model 28″ is tilted away from the lateral side 1487 ofthe knee 1486 such that the joint gap between the femoral condylarsurfaces 1490 (and the tibia condylar surfaces 1491 on the lateral side1487 is greater than the joint gap on the medial side 1485.

As indicated in FIG. 14H, which illustrates the tibia in a coronal crosssection, the line 1495 may be employed to restore the joint line of theknee 1486. The line 1495 may be caused to extend across each of lowestextremity points 1496, 1497 of the respective femoral lateral and medialcondyles 1498, 1499. In this femur bone model 28′, line 1495 may bepresumed to be parallel or nearly parallel to the joint line of the knee1486.

As illustrated in FIG. 14H, the medial gap Gp2 represents the distancebetween the distal femoral medial condyle 1499 and the proximal tibiamedial plateau 1477. The lateral gap Gp1 represents the distance betweenthe distal femoral lateral condyle 1498 and the proximal tibia lateralplateau 1478. In this example illustrated in FIG. 14H, the lateral gapGp1 is significantly larger than the medial gap Gp2 due to degenerationcaused by injury, OA, or etc., that occurred in the lateral side 1487 ofthe knee 1486. It should be noted that the alignment of the bone models28′, 28″ relative to each other for the example illustrated in FIGS. 14Gand 14H depict the alignment the actual bones have relative to eachother in a deteriorated state. To restore the joint line reference andmaintain ligament balancing for the medial collateral ligament (MCL) andlateral collateral ligament (LCL), the joint line gap Gp3 that isdepicted in FIG. 14I, which is the same view as FIG. 14G, except withthe joint line gap Gp3 in a restored state, may be used for the jointspacing compensation adjustment as described below. As illustrated inFIG. 14I, the lines 1495 and 1476 respectively extend across the mostdistal contact points 1496, 1497 of the femur condyles 1498, 1499 andthe most proximal contact points 1466, 1467 of the tibia plateaucondyles 1477, 1478.

For calculation purposes, the restored joint line gap Gp3 may bewhichever of Gp1 and Gp2 has the minimum value. In other words, therestored joint line gap Gp3 may be as follows: Gp3=MIN (Gp1, Gp2). Forpurposes of the adjustment for joint spacing compensation, theadjustment value tr may be calculated as being half of the value forGp3, or in other words, tr-Gp3/2. As can be understood from FIGS.14G-14H and 14J, in this example, the non-deteriorated side 1485 hasGp2, which is the smallest joint line gap and, therefore. Gp3=Gp2 in theexample depicted in FIG. 14G-14J, and tr=Gp2/2.

In one embodiment, the joint line gap assessment may be at least a partof a primary assessment of the geometry relationship between the distalfemur and proximal tibia. In such an embodiment, the joint gapassessment step may occur prior to the femur planning steps of the POPprocess. However, in other embodiments, the joint line gap assessmentmay occur at other points along the overall POP process.

b. Determine Compensation for Joint Spacing

Once the adjustment value tr is determined based off of cartilagethickness or joint line gap Gp3, the planning for the femoral implantmodel 34′ can be modified or adjusted to compensate for the jointspacing in order to restore the joint line. As shown in FIG. 15, whichis a 3D coordinate system wherein the femur reference data 100 is shown,the compensation for the joint spacing is performed both in distal andposterior approaches. Thus, the joint compensation points relative tothe femur reference data are determined. As will be discussed later inthis Detailed Description, the joint compensation points relative to thefemur reference data will be used to determine the joint compensationrelative to the femur implant.

As can be understood from FIG. 16, which is a y-z plane wherein thejoint compensation points are shown, the posterior plane S and thedistal plane P are moved away in the direction of normal of plane S andP respectively by the adjustment value tr. In one embodiment, theadjustment value tr is equal to the cartilage thickness. That is, thejoint compensation points will be determined relative to the posteriorplane S and the distal plane P which are moved away in the direction ofnormal of plane S and P, respectively, by an amount equal to thecartilage thickness. In some embodiments, the adjustment value tr isequal to one-half of the joint spacing. That is, the joint compensationpoints will be determined relative to the posterior plane S and thedistal plane P which are moved away in the direction of normal of planeS and P, respectively, by an amount equal one-half the joint spacing. Inother words, the femoral implant accounts for half of the joint spacingcompensation, while the tibia implant will account for the other half ofthe joint spacing compensation.

As can be understood from FIG. 15, the femur reference data 100 wasuploaded onto a coordinate system, as described above. To compensate forthe joint spacing, the distal line-D₁D₂ is moved closer to the distalplane-P by an amount equal to the adjustment value tr, thereby resultingin joint spacing compensation points D_(1J), D_(2J) and lineD_(1J)D_(2J). The distal plane P was previously moved by adjustmentvalue tr. Similarly, posterior reference line P₁P₂ is moved closer tothe posterior plane-S by an amount equal to the adjustment value tr,thereby resulting in joint spacing compensation points P_(1J), P_(2J)and line P_(1J)P_(2J). The trochlear groove reference line-line GO doesnot move and remains as the reference line for the joint spacingcompensation. Lines D_(1J)D_(2J) and P_(1J)P_(2J) will be stored andutilized later for an analysis related to the femoral implant silhouettecurve.

4. Selecting the Sizes for the Femoral Implants

The next steps are designed to select an appropriate implant size suchthat the implant will be positioned within the available degrees offreedom and may be optimized by 2D optimization. There are 6 degrees offreedom for a femoral implant to be moved and rotated for placement onthe femur. For example, the translation in the x direction is fixedbased on the reference planes-S and P and sagittal slices of femur asshown in FIGS. 4 and 7C. Rotation around the y axis, which correspondsto the varus/valgus adjustment is fixed based on the reference linesdetermined by analysis of the coronal slices, namely, lines EF and AB,and coronal plane-S as shown in FIGS. 4 and 7B. Rotation around the zaxis, which corresponds to internal/external rotation, is fixed by thetrochlear groove reference line, line GO or TGB, axial-distal referenceline, line CD, and axial-posterior reference line, line AB, as shown inthe axial views in FIGS. 4 and 6A-6E. By fixing these three degrees offreedom, the position of the implant can be determined so that the outersilhouette line of the implant passes through both the distal referenceline and posterior reference line. Optimization will search for asub-optimal placement of the implant such that an additional angle offlange contact is greater than but relatively close to 7 degrees. Thus,by constraining the 3 degrees of freedom, the appropriate implant can bedetermined.

a. Overview of Selection of Femoral Implant

Based on previously determined femoral implant data 100′, as shown inFIGS. 11-13, a set of 3 possible sizes of implants are chosen. For eachimplant, the outer 2D silhouette curve of the articular surface of thecandidate implant model is computed and projected onto a y-z plane, asshown in FIGS. 20A-20C. The calculated points of the silhouette curveare stored. Then, the sagittal slice corresponding to the inflectionpoint 500 (see FIG. 21A) is found and the corresponding segmentationspline is considered and the information is stored. Then an iterativeclosest point alignment is devised to find the transform to match theimplant to the femur.

The next sections of this Detailed Description will now discuss theprocess for determining the appropriate implant candidate, withreference to FIGS. 17-22.

i. Implant Selection

In one embodiment, there is a limited number of sizes of a candidatefemoral implant. For example, one manufacturer may supply six sizes offemoral implants and another manufacturer may supply eight or anothernumber of femoral implants. A first implant candidate 700 (see FIG. 17)may be chosen based on the distance L′ between the posterior and distalreference lines P₁′P₂′ and D₁′D₂′ determined above in FIG. 13, withreference to the femoral implant reference data 100′. The distance L′ ofthe candidate implants may be stored in a database and can be retrievedfrom the implant catalogue. In some embodiments, a second and thirdimplant candidate 702, 704 (not shown) may be chosen based on thedistance L between the posterior and distal reference lines P₁P₂ and D₁D₂ of the femur 28′ determined above in FIG. 8, with reference to thefemoral reference data 100 and distance L′. First implant candidate 700has the same distance L as the patient femur. Second implant candidate702 is one size smaller than the first implant candidate 700. Thirdimplant candidate 704 is one size larger than the first implantcandidate 700. In some embodiments, more than 3 implant candidates maybe chosen.

The following steps 2-6 are performed for each of the implant candidates700, 702, 704 in order to select the appropriate femoral implant 34′.

ii. Gross Alignment of Implant onto Femur

In some embodiments, the gross alignment of the implant 34′ onto thefemur 28′ may be by comparison of the implant reference data 100′ andthe femur reference data 100. In some embodiments, gross alignment maybe via comparison of the medial-lateral extents of both the implant andthe femur. In some embodiments, both gross alignment techniques may beused.

In some embodiments, as shown in FIG. 17, which shows the implant 34′placed onto the same coordinate plane with the femur reference data 100,the implant candidate may be aligned with the femur. Alignment with thefemur may be based on the previously determined implant reference linesD₁′D₂′ and P₁′P₂′ and femur reference lines D₁D₂ and P₁P₂.

In some embodiments, and as can be understood from FIGS. 18A-18C and19A-19C, the medial lateral extent of the femur and the implant can bedetermined and compared to ensure the proper initial alignment. FIG. 18Ais a plan view of the joint side 240 of the femur implant model 34′depicted in FIG. 3B. FIG. 18B is an axial end view of the femur lowerend 200 of the femur bone model 28′ depicted in FIG. 3A. The viewsdepicted in FIGS. 18A and 18B are used to select the proper size for thefemoral implant model 34′.

As can be understood from FIG. 18A, each femoral implant available viathe various implant manufacturers may be represented by a specificfemoral implant 3D computer model 34′ having a size and dimensionsspecific to the actual femoral implant. Thus, the representative implantmodel 34′ of FIG. 18A may have an associated size and associateddimensions in the form of, for example, an anterior-posterior extent iAPand medial-lateral extent iML, which data can be computed and stored ina database. These implant extents iAP, iML may be compared to thedimensions of the femur slices from the patient's actual femur 18. Forexample, the femur bone 18 may have dimensions such as, for example, ananterior-proximal extent bAP and a medial-lateral extent bML, as shownin FIG. 18B. In FIG. 18A, the anterior-posterior extent iAP of thefemoral implant model 34′ is measured from the anterior edge 270 to theposterior edge 275 of the femoral implant model 34′, and themedial-lateral extent iML is measured from the medial edge 280 to thelateral edge 285 of the femoral implant model 34′.

Each patient has femurs that are unique in size and configuration fromthe femurs of other patients. Accordingly, each femur slice will beunique in size and configuration to match the size and configuration ofthe femur medically imaged. As can be understood from FIG. 18B, thefemoral anterior-posterior length bAP is measured from the anterior edge290 of the patellofemoral groove to the posterior edge 295 of thefemoral condyle, and the femoral medial-lateral length bML is measuredfrom the medial edge 300 of the medial condyle to the lateral edge 305of the lateral condyle. The implant extents iAP and iML and the femurextents bAP bML may be aligned for proper implant placement as shown inFIG. 18C and along the direction of axial-distal reference line-CD.

As can be understood from FIGS. 19A-19C, these medial-lateral extents ofthe implant iML and femur bML can be measured from the 2D slices of thefemur of FIG. 5A. For example, FIG. 19A, which shows the most medialedge of the femur in a 2D sagittal slice and FIG. 19B, which shows themost lateral edge of the femur in a 2D sagittal slice, can be used tocalculate the bML of the femur 28′. The implant 34′ will be centeredbetween the medial and lateral edges, as shown in FIG. 19C, which is a2D slice in coronal view showing the medial and lateral edges, therebygrossly aligning the implant with the femur.

iii. Determine Outer Silhouette Curve of Implant in Y-Z Plane

The silhouette of the femoral implant is the curve formed by farthestpoints from center in y-z plane projection of the femoral implantgeometry. The points of the silhouette curve may be utilized to confirmplacement of the implant onto the femur based on the femur referencelines that have been altered to account for the joint compensation.

For a discussion of the process for determining the points of thesilhouette curve of the femoral implant, reference is now made to FIGS.20A-20C. As can be understood from FIG. 20A, which is an implant 34′mapped onto a y-z plane, the points of a candidate implant are retrievedfrom the implant database. The points are then imported onto a y-z planeand the silhouette curve can be determined. The silhouette curve 34′″ isdetermined by finding the points that are the farthest from the centeralong an outer circumference 35 of the articular surface of the implant34′. FIG. 20B, which is the silhouette curve 34′″ of the implant 34′,shows the result of the silhouette curve calculations. The silhouettecurve data is then imported into a y-z plane that includes the jointspacing compensation data, as shown in FIG. 20C, which is the silhouettecurve 34′″ aligned with the joint spacing compensation pointsD_(1J)D_(2J) and P_(1J)P_(2J). The resulting joint spacing compensationand silhouette curve data 800 (e.g. D₁′″D₂′″P₁′″P₂′″) is stored forlater analysis.

iv. Determination of Inflection Point, Flange Point, Femur Spline andAnterior Femur Cut Plane

The flange point is determined and stored. As can be understood fromFIG. 21A, which shows a distal femur 28′ with an implant 34′, the distalfemur is analyzed and the flange point 500 of the implant 34′ isdetermined relative to the anterior surface 502 of the distal end of afemur condyle 28′. FIG. 21B, which depicts a femur implant 34′,illustrates the location of the flange point 500 on the implant 34′ asdetermined by an analysis such as one illustrated in FIG. 21A.

The anterior cut plane 504 is determined and stored. The range of theanterior cut plane of the implant is determined such that the cut plane(and therefore the implant) is within certain tolerances. As shown inFIG. 21A, a cut plane 504 is determined based on the location of theimplant 34′ on the femur 28′. An angle A between the cut plane 504 andthe flange point 500 is between approximately 7 and approximately 15degrees. In some embodiments, the angle A is approximately 7 degrees. Insome embodiments, the distal cut plane may be found as described belowwith respect to the final verification step. For each respectiveimplant, the anterior cut plane and the distal cut plane are at a fixedangle for the implant. That is, once the anterior cut plane is found,the distal cut plane can be determined relative to the fixed angle andthe anterior cut plane. Alternatively, once the distal cut plane isfound, the anterior cut plane can be determined relative to the fixedangle and the distal cut plane.

The inflection point 506 is determined and stored. As shown in FIG. 21C,which shows a slice of the distal femur 28′ in the sagittal view, theinflection point 506 is located on the anterior shaft of the spline 508of femur 28′ where the flange point 500 of the implant 34′ is in contactwith the femur 28′. An implant matching algorithm will match the flangepoint 500 of implant 34′ to the spline 508 of the femur at approximatelythe inflection point 506 of the femur 28′. As can be understood fromFIG. 21D, which shows the implant 34′ positioned on the femur 28′, theimplant 34′ should be aligned to touch the distal and posteriorreference planes P. S respectively to reach proper alignment. In oneembodiment, the implant matching algorithm is a customized extension ofan algorithm known as iterative closest point matching.

The next section of the Detailed Description now discusses how the dataand data points determined above and stored for future analysis will beused in the selection of an appropriate implant.

v. Determine Points of Set A and Set B

Determination of the data sets contained in Set A and Set B aid indetermining the appropriate implant and ensuring that the chosen implantmates with the femur within certain tolerances.

The joint spacing compensation points D_(1J)D_(2J) and P_(1J)P_(2J) weredetermined as described with reference to FIG. 16 and are added to SetA. Next, the joint spacing compensation points D_(1J)D_(2J) andP_(1J)P_(2J) are matched to the closest respective points on thesilhouette curve, as shown in FIG. 20C, thereby resulting in pointsD₁′″D₂′″ and P₁′″P₂′″ or the joint spacing compensation and silhouettecurve data 800. Points D₁′″D₂′″ and P₁′″P₂′″ will be added to Set B.

The inflection point and flange point data are analyzed. An inflectionpoint 506′ is found to represent the inflection point 506 that isclosest in proximity to the flange point 500, which were both discussedwith reference to FIGS. 21A-21D. The point 506′ is added to Set A. Theflange point 500 is then projected to a y-z plane. The resulting flangepoint 500′ is added to Set B.

Thus, Set A contains the following points: the joint spacingcompensation points D_(1J)D_(2J) and P_(1J)P_(2J) and the inflectionpoint 506′. Set B contains the following points: Points D₁′″D₂′″ andP₁′″P₂′″ (the joint spacing compensation and silhouette curve data 800)and the flange point 500′.

vi. Utilize the Data of Sets A and B

Find a rigid body transform. The data points of Set A and Set B arecompared and a rigid body transform that most closely matches Set A toSet B is chosen. The rigid body transform will transform an objectwithout scaling or deforming. That is, the rigid body transform willshow a change of position and orientation of the object. The chosentransform will have rotation about the x-axis and translation in the y-zplane.

Find the inverse of the rigid body transform. The inverse of this rigidbody transform is then imported into the y-z plane that also containsthe femur reference lines D₁D₂ anti P₁P₂ and the femur spline 508 thatcorresponds to the flange point 500 of the implant 34′.

The steps described in subsections iv, v and vi of subsection D4(a) ofthis Detailed Description are repeated until the relative motion iswithin a small tolerance. In one embodiment, the steps are repeatedfifty times. In some embodiments, the steps are repeated more than fiftytimes or less than fifty times.

In some embodiments, and as shown in FIG. 22A, an acceptable translationin y-z plane may be determined. FIG. 22A depicts an implant that isimproperly aligned on a femur, but shows the range of the search for anacceptable angle A. Within this range for angle A, the translation iny-z leads to finding the rigid body transform as described above. Insome embodiments, the process may optimize y-z translation and rotationaround the x-axis in one step. This can be done by rotating the implantsilhouette curve by several half degree increments and then, for eachincrement, performing the steps described in subsections iv, v and vi ofsubsection D4(a) of this Detailed Description. Translation in the y-zaxis only occurs during the analysis utilizing the inverse of the rigidbody transform.

vii. Additional Verification and Confirmation of Femur Cut Plane

By using the above outlined procedure, an appropriate implant is foundby choosing the implant and transform combination that provides aninflection angle that is greater than 7 degrees but closest to 7degrees, as explained with reference to FIG. 21A.

In some embodiments, an additional verification step is performed byplacing the implant 34′ in the MRI with the transform 28′″ that is foundby the above described method. As can be understood from FIG. 22B, whichillustrates the implant positioned on the femur transform wherein afemur cut plane is shown, during the verification step, a user maydetermine the amount of bone that is cut J₁ on the medial and lateralcondyles by looking at the distal cut plane 514 of the implant 34′, J₁is determined such that the thickness of the bone cut on both the medialand lateral sides is such that the bone is flat after the cut. Multipleslices in both the distal and medial areas of the bone can be viewed toverify J₁ is of proper thickness.

Once an appropriate femur implant is chosen, the preoperative planningprocess turns to the selection of an appropriate tibia implant. Thetibia planning process includes a determination of the tibia referencelines to help determine the proper placement of the tibia implant. Thecandidate tibia implant is placed relative to the tibia reference linesand placement is confirmed based on comparison with several 2Dsegmentation splines.

E. Tibia Planning Process

For a discussion of the tibia planning process, reference is now made toFIGS. 23-32D. FIGS. 23-26B illustrate a process in the POP wherein thesystem 10 utilizes 2D imaging slices (e.g., MRI slices, CT slices, etc.)to determine tibia reference data, such as reference points andreference lines, relative to the undamaged side of the tibia plateau.The resulting tibia reference data 900 is then mapped or projected to anx-y plane (axial plane). A candidate tibia implant is chosen, whichselection will be discussed with reference to FIGS. 27A-C. The tibiaimplant placement is adjusted and confirmed relative to the tibia, asdiscussed in more detail below with reference to FIGS. 28-32D.

1. Determining Tibia Reference Data

For a discussion of a process used to determine the tibia reference data900, reference is now made to FIGS. 23-27B. As can be understood fromFIG. 23, which is a top view of the tibia plateaus 404, 406 of a tibiabone image or model 28″, the tibia reference data 900 may includereference points (e.g. Q₁, Q₁′), reference lines (e.g. T₁T₂, V₁) and areference plane (e.g. S′) (see FIGS. 26A-26B). In some embodiments, thetibia reference data 900 may also include the anterior-posterior extant(tAP) and the medial-lateral extant (tML) of the tibia 28″ (see FIGS.27A-27B). As shown in FIG. 23, each tibia plateau 404, 406 includes acurved recessed condyle contacting surface 421, 422 that is generallyconcave extending anterior/posterior and medial/lateral. Each curvedrecessed surface 421, 422 is generally oval in shape and includes ananterior curved edge 423, 424 and a posterior curved edge 425, 426 thatrespectively generally define the anterior and posterior boundaries ofthe condyle contacting surfaces 421, 422 of the tibia plateaus 404, 406.Depending on the patient, the medial tibia plateau 406 may have curvededges 424, 426 that are slightly more defined than the curved edges 423,425 of the lateral tibia plateau 404.

a. Identify Points Q1, Q2 and Q1′, Q2′

2D slices in the sagittal view are analyzed to determine the tibiaflexion/extension adjustment. Anterior tangent lines T_(Q1), T_(Q2) canbe extended tangentially to the most anterior location on each anteriorcurved edge 423, 424 to identify the most anterior points Q1. Q2 of theanterior curved edges 423, 424. Posterior tangent lines T_(Q1)′, T_(Q2)′can be extended tangentially to the most posterior location on eachposterior curved edge 425, 426 to identify the most posterior pointsQ1′, Q2′ of the posterior curved edges 425, 426. Thus, in oneembodiment, the lateral side tibia plateau 404 can be analyzed viatangent lines to identify the highest points Q1, Q1′. For example,tangent line TQ1 can be used to identify the anterior highest point Q1,and tangent line T_(Q1)′ can be used to identify the posterior highestpoint Q1′. In some embodiments, a vector V1 extending between thehighest points Q1, Q1′ may be generally perpendicular to the tangentlines T_(Q1), T_(Q1)′. Similarly, the medial side tibia plateau 406, canbe analyzed via tangent lines to identify the highest points Q2, Q2′.For example, tangent line T_(Q2) can be used to identify the anteriorhighest point Q2, and tangent line TQ2′ can be used to identify theposterior highest point Q2′. In some embodiments, a vector V2 extendingbetween the highest points Q2, Q2′ may be generally perpendicular to thetangent lines T_(Q2), T_(Q2)′.

i. Confirm points Q1, Q2 and Q1′, Q2′

As can be understood from FIGS. 24A-24D, the location of Q1, Q1′, Q2 andQ2′ may also be confirmed by an analysis of the appropriate sagittalslice. As shown in FIG. 24A, which is a sagittal cross section through alateral tibia plateau 404 of the tibia model or image 28′, points Q1 andQ1′ can be identified as the most anterior and posterior points,respectively, of the curved recessed condyle contacting surface 421 ofthe lateral tibia plateau 404. As shown in FIG. 24B, which is a sagittalcross section through a medial tibia plateau 406 of the tibia model 28″,points Q2 and Q2′ can be identified as the most anterior and posteriorpoints, respectively, of the curved recessed condyle contacting surface422 of the medial tibia plateau 406. Such anterior and posterior pointsmay correspond to the highest points of the anterior and posteriorportions of the respective tibia plateaus.

b. Determine Lines V1 and V2

As can be understood from FIGS. 23-24B, line V1 extends through anteriorand posterior points Q1, Q1′, and line V2 extends through anterior andposterior points Q2. Q2′. Line V1 is a lateral anterior-posteriorreference line. Line V2 is a medial posterior-anterior reference line.Each line V1, V2 may align with the lowest point of theanterior-posterior extending groove/valley that is the ellipticalrecessed tibia plateau surface 421, 422. The lowest point of theanterior-posterior extending groove/valley of the elliptical recessedtibia plateau surface 421, 422 may be determined via ellipsoid calculus.Each line V1. V2 will be generally parallel to the anterior-posteriorextending valleys of its respective elliptical recessed tibia plateausurface 421, 422 and will be generally perpendicular to its respectivetangent lines T_(Q1), T_(Q1)′, T_(Q2), T_(Q2)′. The anterior-posteriorextending valleys of the elliptical recessed tibia plateau surfaces 421,422 and the lines V1, V2 aligned therewith may be generally parallel.The planes associated with lines V1 and V2 are generally parallel ornearly parallel to the joint line of the knee joint, as determinedabove.

Depending on the patient, the medial tibia plateau 406 may be undamagedor less damaged than the lateral tibia plateau 404. In such a case, thereference points Q2. Q2′ and reference line V2 of the medial plateau 406may be used to establish one or more reference points and the referenceline of the damaged lateral tibia plateau. FIG. 24C depicts a sagittalcross section through an undamaged or little damaged medial tibiaplateau 406 of the tibia model 28″, wherein osteophytes 432 are alsoshown. As indicated in FIG. 24C, the points Q2. Q2′ can be located onthe undamaged medial plateau and set as reference points. Theanterior-posterior reference line, line V2, can be constructed byconnecting the anterior and posterior reference points Q2. Q2′. Thereference line V2 from the undamaged or little damaged medial side issaved for use in determining the reference line of the lateral tibiaplateau in the case where the lateral tibia plateau is damaged. Forexample, as shown in FIG. 24D, which is a sagittal cross section througha damaged lateral tibia plateau 404 of the tibia model 28″, the anteriorpoint Q1 is found to be undamaged. In this case, the establishedreference line V2 from the medial plateau can be applied to the damagedlateral plateau by aligning the reference line V2 with point Q1. Bydoing so, the reference line V1 of the lateral plateau can beestablished such that line V1 touches the reference point Q1 and extendsthrough the damaged area 403. Thus, the reference line V1 in the lateralplateau is aligned to be parallel or nearly parallel to the referenceline V2 in the medial plateau. While the above described process isdescribed in terms of extrapolating one or more reference lines of adamaged lateral plateau from an analysis of the undamaged medial tibiaplateau, it is understood that the same process can be undertaken wherethe lateral tibia plateau is undamaged and one or more reference linesof a damaged medial plateau can be extrapolated from the lateral tibiaplateau.

In other embodiments, as can be understood from FIG. 24D and assumingthe damage to the lateral tibia plateau 404 is not so extensive that atleast one of the highest anterior or posterior points Q1, Q1′ stillexists, the damaged tibia plateau 404 can be analyzed via tangent linesto identify the surviving high point Q1, Q1′. For example, if the damageto the lateral tibia plateau 404 was concentrated in the posteriorregion such that the posterior highest point Q1′ no longer existed, thetangent line T_(Q1) could be used to identify the anterior highest pointQ1. Similarly, if the damage to the medial tibia plateau 406 wasconcentrated in the anterior region such that the anterior highest pointQ1′ no longer existed, the tangent line T_(Q1)′ could be used toidentify the posterior highest point Q1′. In some embodiments, a vectorextending between the highest points Q1, Q1′ may be generallyperpendicular to the tangent lines T_(Q1), T_(Q1)′.

c. Determine Reference Points T1 and T2 and Reference Line T1T2

2D slices in both the axial and coronal views are analyzed to determinethe varus/valgus adjustment by finding the reference points T1 and T2.As shown in FIGS. 25A-25B, which are coronal and axial 2D slices of thetibia, reference points T1 and T2 are determined by an analysis of themost proximal coronal slice (FIG. 25A) and the most proximal axial slice(FIG. 25B). As indicated in FIG. 25A, in which the tibia is shown in a0° knee extension, reference points T1 and T2 are determined. The pointsT1 and T2 represent the lowest extremity of tangent contact points oneach of the lateral and medial tibia plateaus, respectively. In oneembodiment, tangent points T1 and T2 are located within the regionbetween the tibia spine and the medial and lateral epicondyle edges ofthe tibia plateau, where the slopes of tangent lines in this region aresteady and constant. For example, and as shown in FIG. 25A, the tangentpoint T1 is in the lateral plateau in Area I between the lateral side ofthe lateral intercondylar tubercle to the attachment of the lateralcollateral ligament. For the medial portion, the tangent point T2 is inArea II between the medial side of the medial intercondylar tubercle tothe medial condyle of the tibia.

As shown in FIG. 25B, the most proximal slice of the tibia in the axialview is analyzed to find reference points T1 and T2. As above, referencepoints T1 and T2 represent the lowest extremity of tangent contactpoints on each of the lateral and medial tibia plateaus. Once thereference points T1 and T2 are found in both the coronal and axialviews, a line T1T2 is found.

A line T1T2 is created by extending a line between reference points T1and T2. In some embodiments, the coronal and axial slices are viewedsimultaneously in order to align the lateral and medialanterior-posterior reference lines V1 and V2. As shown in FIG. 23, thelateral and medial anterior-posterior reference lines V1 and V2 aregenerally perpendicular or nearly perpendicular to line T1T2.

d. Determine the Approximate ACL Attachment Point (AE) and theApproximate PCL Attachment Point (PE) of the Tibia and Reference LineAEPE

As can be understood from FIGS. 23 and 25B, the reference pointsrepresenting the approximate anterior cruciate ligament (ACL) attachmentpoint of the tibia AE and the approximate posterior cruciate ligament(PCL) attachment point of the tibia PE are determined. The referencepoint AE can be determined by finding the approximate tibia attachmentpoint for the ACL. The reference point PE can be determined by findingthe approximate tibia attachment point for the PCL. The line AEPEconnects through reference points AE and PE and may also be referred toas an ACL/PCL bisector line.

e. Confirm Location of Tibia Reference Data

As can be understood from FIG. 23, the tibia reference data 900 includesreference points and reference lines that help to defineflexion/extension adjustment, varus/valgus adjustment andinternal/external rotation. For example, the tibia flexion/extensionadjustment is determined by an analysis of the sagittal images as shownin FIGS. 24A-D, which determine reference points Q1, Q1′, Q2, Q2′. Thetibia varus/valgus adjustment may be found by an analysis of FIG. 25Aand finding reference points T1, T2 and reference line T1T2. As can beunderstood from FIG. 23, the proximal reference line, line T1T2, definesthe internal/external rotation as shown in an axial view (line T1T2 inFIG. 25B) and the varus/valgus angle as shown in a coronal view (lineT1T2 in FIG. 25A).

The location of the reference points and reference lines may also beconfirmed based on their spatial relationship to each other. Forexample, as shown in FIGS. 23-24B, the anterior-posterior referencelines V1, V2 of the tibia plateau are generally parallel to the ACL/PCLbisector reference line, line AEPE. As indicated in FIGS. 23 and 25B,the axial-proximal reference line, line T1T2 is perpendicular or nearlyperpendicular to anterior-posterior reference lines V1. V2. As shown inFIG. 23, the tangent lines T_(Q1), T_(Q2), T_(Q1)′, T_(Q2)′ areperpendicular or nearly perpendicular to the ACL/PCL bisector referenceline, line AEPE.

f. Mapping the Tibia Reference Data to an x-y Plane

As can be understood from FIGS. 26A-26B, which depict the tibiareference data 900 on a coordinate system (FIG. 26A) and on a proximalend of the tibia (FIG. 26B), the tibia reference data 900 is mapped toan x-y coordinate system to aid in the selection of an appropriate tibiaimplant. As shown in FIG. 26A, the endpoints Q1. Q1′. Q2. Q2′ and theirrespective anterior posterior reference lines V1 and V2 and theendpoints T1, T2 and the proximal reference line T1T2 are each mapped tothe reference plane. In addition, and as shown in FIG. 26B, thereference data 900 may be imported onto a 3D model of the tibia 28″ forverification purposes. The tibia reference data 900 is stored for lateranalysis.

2. Selecting Tibia Implant Candidate

There are six degrees of freedom for placing the tibial implant onto thetibia. The reference points and reference lines determined above willconstrain all but 2 degrees of freedom which are translated in the x-yplane. The sizing and positioning of the tibia implant (and the femoralcomponent) will be verified with a 2D view of the knee and components.

As briefly discussed above with reference to FIGS. 1A and 1C, whenselecting the tibia implant model 34″ corresponding to the appropriatetibia implant size to be used in the actual arthroplasty procedure, thesystem 4 may use one of at least two approaches to select theappropriate size for a tibia implant [block 115]. In one embodiment, thetibia implant is chosen based on the size of the femoral implant thatwas determined above. In some embodiments, as discussed with referenceto FIGS. 27A-27C, the system 4 determines the tibial anterior-posteriorlength tAP and the tibial medial-lateral length tML and the tibiaimplant 34″ can be selected based on the anterior-posterior extent tAPof the proximal tibia. In some embodiments, the tibia implant may beselected based on both the tibial anterior-posterior length tAP and thetibial medial-lateral length tML.

In one embodiment, there is a limited number of sizes of a candidatetibia implant. For example, one manufacturer may supply six sizes oftibia implants and another manufacturer may supply eight or anothernumber of tibia implants. The anterior-posterior length jAP andmedial-lateral length jML dimensions of these candidate implants may bestored in a database. The tAP and tML are compared to the jAP and jML ofcandidate tibia implants stored in the database.

FIG. 27A is a 2D sagittal image slice of the tibia wherein asegmentation spline with an AP extant is shown. FIG. 27B is an axial endview of the tibia upper end of the tibia bone image or model 28″depicted in FIG. 3A. FIG. 27C is a plan view of the joint side 255 ofthe tibia implant model 34″ depicted in FIG. 3B. The views depicted inFIGS. 27A-27C are used to select the proper size for the tibial implantmodel 34″. The tibia implant may be chosen based on the maximum tAPextent as measured in an analysis of the segmentation spine as shown inFIG. 27A.

Each patient has tibias that are unique in size and configuration fromthe tibias of other patients. Accordingly, each tibia bone model 28″will be unique in size and configuration to match the size andconfiguration of the tibia medically imaged. As can be understood fromFIG. 27B, the tibial anterior-posterior length tAP is measured from theanterior edge 335 of the tibial bone model 28″ to the posterior edge 330of the tibial bone model 28″, and the tibial medial-lateral length tMLis measured from the medial edge 340 of the medial plateau of the tibiabone model 28″ to the lateral edge 345 of the lateral plateau of thetibia bone model 28″.

As can be understood from FIG. 27C, each tibial implant available viathe various implant manufacturers may be represented by a specific tibiaimplant 3D computer model 34″ having a size and dimensions specific tothe actual tibia implant. Thus, the representative implant model 34″ ofFIG. 3D may have an associated size and associated dimensions in theform of, for example, anterior-proximal extent tAP and themedial-lateral extent tML of the tibia model 34″, as shown in FIG. 27B.In FIG. 27C, the anterior-posterior extent jAP of the tibia implantmodel 34″ is measured from the anterior edge 315 to the posterior edge310 of the tibial implant model 34″, and the medial-lateral extent jMLis measured from the medial edge 320 to the lateral edge 325 of thetibial implant model 34″. Once the tibia implant candidate 34″ ischosen, the reference lines jML, jAP of the implant candidate 34″ arestored by the system 4 for later analysis.

3, Determine Tibia Implant Reference Data

As can be understood from FIG. 28, which is a top view of the tibiaplateaus 404′, 406′ of a tibia implant model 34″, wherein the tibiaimplant reference data 900′ is shown, the tibia reference data 900′ mayinclude tangent points q1, q1′, q2, q2′ and correspondinganterior-posterior reference lines V3. V4 and intersection points t1, t2and its corresponding proximal reference line t1t2.

In order to define the implant reference data 900′ relative to the tibiamodel 28″, the implant reference lines jML, jAP are imported into thesame x-y plane with the tibia reference data 900 that was previouslymapped to the x-y plane. For gross alignment purposes, themedial-lateral extent jML of the tibia implant 34″ is aligned with theproximal reference line T1T2 of the tibia model 28″. Then, the tibiareference data 900′ is determined. The implant 34″ and the bone model28″ may then undergo additional alignment processes.

a. Determine Tangent Points q1, q1′, q2, q2′

As shown in FIG. 28, each tibia plateau 404′, 406′ includes a curvedrecessed condyle contacting surface 421′, 422′ that is generally concaveextending anterior/posterior and medial/lateral. Each curved recessedsurface 421′, 422′ is generally oval in shape and includes an anteriorcurved edge 423′, 424′ and a posterior curved edge 425′, 426′ thatrespectively generally define the anterior and posterior boundaries ofthe condyle contacting surfaces 421′, 422′ of the tibia plateaus 404′,406′. Thus, the lateral tangent points q1, q1′ can be identified as themost anterior and posterior points, respectively, of the curved recessedcondyle contacting surface 421′ of the lateral tibia plateau 404′. Themedial tangent points q2, q2′ can be identified as the most anterior andposterior points, respectively, of the curved recessed condylecontacting surface 422′ of the medial tibia plateau 406′.

b. Determine Reference Lines V3 and V4

As can be understood from FIG. 28, line V3 extends through anterior andposterior points q1, q1′, and line V4 extends through anterior andposterior points q2, q2′. Line V3 is a lateral anterior-posteriorreference line. Line V4 is a medial posterior-anterior reference line.Each line V3, V4 may align with the lowest point of theanterior-posterior extending groove/valley that is the ellipticalrecessed tibia plateau surface 421′, 422′. The lowest point of theanterior-posterior extending groove/valley of the elliptical recessedtibia plateau surface 421′, 422′ may be determined via ellipsoidcalculus. Each line V3, V4 will be generally parallel to theanterior-posterior extending valleys of its respective ellipticalrecessed tibia plateau surface 421′, 422′. The length of the referencelines V3. V4 can be determined and stored for later analysis.

c. Determine Intersection Points t1, t2 and Implant Proximal ReferenceLine t1t2

As shown in FIG. 28, the intersection or reference points t1, t2represent the midpoints of the respective surfaces of the lateral tibiaplateau 404′ and the medial tibia plateau 406′. Also, each intersectionpoint t1, t2 may represent the most distally recessed point in therespective tibia plateau 404′, 406′. An implant proximal reference linet1t2 is created by extending a line between the lateral and mediallowest reference points t1, t2. The length of the reference line t1t2can be determined and stored for later analysis. This line t1t2 isparallel or generally parallel to the joint line of the knee. Also, asindicated in FIG. 28, the tibia implant 34″ includes a base member 780for being secured to the proximal tibia 28″.

d. Align Implant Reference Data 900′ with Tibia Reference Data 900

As can be understood from FIGS. 28 and 26A, the implant reference data900′ specifies the position and orientation of the tibia implant 34″ andgenerally aligns with similar data 900 from the tibia bone model 28″.Thus, the lateral tangent points q1, q1′ and medial tangent points q2,q2′ of the implant 34″ generally align with the lateral tangent pointsQ1, Q1′ and medial tangent points Q2. Q2′ of the tibia 28″. The anteriorposterior reference lines V3. V4 of the implant 34″ generally align withthe anterior posterior reference lines V1, V2 of the tibia model 28″.The intersection points t1, t2 of the implant 34″ generally align withthe reference points T1, T2 of the tibia 28″. The proximal referenceline t1, t2 of the implant 34″ generally aligns with the proximalreference line T1T2 of the tibia 28″. Reference line t1t2 isapproximately perpendicular to the anterior-posterior reference linesV3. V4.

The implant reference data 900′ lies on a coordinate frame, plane r′.The tibia reference data 900 lies on a coordinate frame, plane s′. Thus,the alignment of the implant 34″ with the tibia 28″ is thetransformation between the two coordinate frames plane r′, plane s′.Thus, the gross alignment includes aligning the proximal line t1t2 ofthe implant 34″ to the proximal line T1T2 of the tibia 28″. Then, in afurther alignment process, the reference points t1, t2 of the implantand the reference points T1, T2 of the tibia 28″ are aligned. Theimplant 34″ is rotated such that the sagittal lines of the implant 34″(e.g. V3. V4) are parallel or generally parallel to the sagittal linesof the tibia 28″ (e.g. V1, V2). Once the tibia 28″ and the implant 34″are in alignment (via the reference data 900, 900′), the tibial cutplane can be determined.

4, Determine Surgical Cut Plane for Tibia

a. Determine Cut Plane of the Tibia Implant

The cut plane of the tibia implant is determined. The user may determinethis cut plane by a method such as one described with respect to FIGS.29A-29C. FIG. 29A is an isometric view of the 3D tibia bone model 1002showing the surgical cut plane SCP design. FIGS. 29B and 29C aresagittal MRI views of the surgical tibia cut plane SCP design with theposterior cruciate ligament PCL.

During the TKA surgery, the damaged bone surface portions of theproximal tibia will be resected from the cut plane level 850 and beremoved by the surgeon. As shown in FIGS. 29B and 29C, the surgicaltibial cut plane 850 may be positioned above the surface where the PCLis attached, thereby providing for the maintenance of the PCL during TKAsurgery.

FIG. 30A is an isometric view of the tibia implant 34″ wherein a cutplane r1 is shown. As can be understood from FIG. 30A, the cut plane r1of the implant 34″ is the surgical tibial cut plane 850 and is a datapoint or set of data points that may be stored in the implant database.In order to determine whether an adjustment to the cut plane r1 must bemade, the cut plane r1 of the tibia implant 34″ is aligned with thetibia 28″.

b. Determine Initial Cut Plane of the Tibia

As shown in FIG. 30B, which is a top axial view of the implant 34″superimposed on the tibia reference data 900, the implant 34″ is openedwith the tibia reference data 900 and is generally aligned with thetibia reference data 900 at the level of the cut plane r1 by the system4. However, the implant 34″ is not centered relative to the tibiareference data 900. The anterior/posterior extent tAP″ andmedial/lateral extent tML″ of the tibia 28″ at the cut level are found.

The implant 34″ may be centered by the system (or manually by a user ofthe system). As indicated in FIG. 30C, which is an axial view of thetibial implant aligned with the tibia reference data 900, the tibiaimplant 34″ is then centered relative to the anterior posterior extenttAP″ and the medial lateral extents tML″ of the tibia 28″.

c. Determine Joint Line and Adjustment

In order to allow an actual physical arthroplasty implant to restore thepatient's knee to the knee's pre-degenerated or natural configurationwith the its natural alignment and natural tensioning in the ligaments,the condylar surfaces of the actual physical implant generally replicatethe condylar surfaces of the pre-degenerated joint bone. In oneembodiment of the systems and methods disclosed herein, condylarsurfaces of the bone model 28″ are surface matched to the condylarsurfaces of the implant model 34″. However, because the bone model 28″may be bone only and not reflect the presence of the cartilage thatactually extends over the pre-degenerated condylar surfaces, the surfacematching of the modeled condylar surfaces may be adjusted to account forcartilage or proper spacing between the condylar surfaces of thecooperating actual physical implants (e.g., an actual physical femoralimplant and an actual physical tibia implant) used to restore the jointsuch that the actual physical condylar surfaces of the actual physicalcooperating implants will generally contact and interact in a mannersubstantially similar to the way the cartilage covered condylar surfacesof the pre-degenerated femur and tibia contacted and interacted.

i. Determine Adjustment Value tr

Thus, in one embodiment, the implant model is modified or positionallyadjusted (via e.g. the tibia cut plane) to achieve the proper spacingbetween the femur and tibia implants. To achieve the correct adjustmentor joint spacing compensation, an adjustment value tr may be determined.In one embodiment, the adjustment value tr that is used to adjust theimplant location may be based off of an analysis associated withcartilage thickness. In another embodiment, the adjustment value tr usedto adjust the implant location may be based off of an analysis of properjoint gap spacing, as described above with respect to FIGS. 14G and 14H.Both of the methods are discussed below in turn.

1. Determining Cartilage Thickness

FIG. 30D is a MRI image slice of the medial portion of the proximaltibia and indicates the establishment of landmarks for the tibia POPdesign. FIG. 30E is a MRI image slice of the lateral portion of theproximal tibia. The wm in FIG. 30D represents the cartilage thickness ofthe medial tibia meniscus, and the wl in FIG. 30E represents thecartilage thickness of the lateral tibia meniscus. In one embodiment,the cartilage thicknesses wl and wm are measured for the tibia meniscusfor both the lateral and medial plateaus 760, 765 via the MRI slicesdepicted in FIGS. 30D and 30E. The measured thicknesses may be compared.If the cartilage loss is observed for the medial plateau 765, then thewl_(min) of lateral plateau 760 is selected as the minimum cartilagethickness. Similarly, if the lateral plateau 760 is damaged due tocartilage loss, then the wm_(min) of medial plateau 765 is selected asthe minimum cartilage thickness. The minimum cartilage wr may beillustrated in the formula, wr=min (wm, wl). In one embodiment, forpurposes of the adjustment to the tibia, the adjustment value tr may bemay be equal to the minimum cartilage value wr.

2. Determining Joint Gap

In one embodiment, the joint gap is analyzed as discussed above withrespect to FIGS. 14G and 14H to determine the restored joint line gapGp3. In one embodiment, for purposes of the adjustment to the tibiashape matching, the adjustment value tr may be calculated as being halfof the value for Gp3, or in other words, tr=Gp3/2.

d. Determine Compensation for Joint Spacing

After centering the implant 34″ within the cut plane, joint spacingcompensation is taken into account. As shown in FIG. 30F, which is anisometric view of the tibia implant and the cut plane, the implant 34″and cut plane-r1 are moved in a direction that is generallyperpendicular to both the proximal and sagittal reference lines by anamount equal to adjustment value tr, thereby creating an adjusted cutplane r1′. In one embodiment, the adjustment value tr is equal toapproximately one-half of the joint spacing. In other embodiments, theadjustment value tr is equal to the cartilage thickness.

Thus, the implant candidate may be selected relative to the jointspacing compensation that was determined previously with reference toFIGS. 14G, 14H, 30D and 30E. As discussed above, in one embodiment, oncethe joint spacing compensation is determined, one-half of the jointspacing compensation will be factored in to the femur planning processand one-half of the joint spacing compensation will be factored in tothe tibia planning process. That is, the femur implant is adjusted by anamount equal to one-half of the joint spacing compensation. Thus, thecandidate femur implant will be chosen such that when it is positionedon the femur relative to the joint spacing compensation, the candidateimplant will approximate the pre-degenerated joint line. Similarly, thetibia implant is adjusted by an amount equal to one-half of the jointspacing compensation. Thus, the candidate tibia implant will be chosensuch that when it is positioned on the tibia relative to the jointspacing compensation, the candidate implant will approximate thepre-degenerated joint line. Also, the tibia implant mounting post 780(see FIG. 31B) and the femur implant mounting post 781 (see FIG. 31A)will be oriented at approximately the center of the tibia and femur.

F. Verification of Implant Planning Models and Generation of SurgicalJigs Based on Planning Model Information

FIGS. 31A1-32 illustrate one embodiment of a verification process thatmay be utilized for the preoperative planning process disclosed herein.FIGS. 31A1-31B are sagittal views of a 2D image slice of the femur 28′(FIGS. 31A1 and 31A2) and the tibia 28″ (FIG. 31B) wherein the 2Dcomputer generated implant models 34 are also shown. As can beunderstood from FIGS. 31A1-31B, verification for both the distal femurand proximal tibia is performed by checking the reference lines/planesin 2D sagittal views. The reference lines/planes may also be checked inother views (e.g. coronal or axial). For example, and as can beunderstood from FIGS. 31A1 and 31A2, for the femur planning model, theflexion-extension rotation is verified by checking whether theinflection point 506 of the anterior cortex of the femur 28′sufficiently contacts the interior surface 510 of the anterior flange512 of implant 34′. That is, as can be understood from FIG. 31A2, whenthe implant 34′ is properly aligned with the femur 28′, the flange point500 of the implant should touch the inflection point of the segmentationspline or femur 28′.

As can be understood with reference to FIG. 31B, the tibia planning maybe verified by looking at a 2D sagittal slice. Depending on the initialplanning choice made above, one of the following can be verified: 1)whether the size of the tibial implant 34″ matches or corresponds withthe size of the femoral implant 34′, or 2) whether the tibial implant34″ is one size larger or one size smaller than the femoral implant 34′size (e.g., a size 2 femur, and a size 1 tibia; or a size 2 femur, and asize 2 tibia; or a size 2 femur, and a size 3 tibia). In otherembodiments, the size of tibial implant may be chosen without takinginto account the size of the femoral implant. One of skill in the artwill recognize that different implant manufacturers may utilize adifferent naming convention to describe different sizes of implants. Theexamples provided herein are provided for illustrative purposes and arenot intended to be limiting.

As indicated in FIG. 31B, the placement of the tibial implant can beverified by viewing the anterior and posterior positions of the implant34″ relative to the tibial bone 28″. If the implant is properlypositioned, the implant should not extend beyond the posterior oranterior edge of the tibia bone. The flexion-extension of the tibia 28″can be verified by checking that the tibial implant reference line 906,which is a line segment approximating the normal direction of theimplant's proximal surface, is at least parallel with the posteriorsurface 904 of the tibia 28″ or converging with the posterior tibialsurface 906 around the distal terminus of the tibial shaft.

In other embodiments, as shown in FIGS. 32A-32G and FIGS. 33A-33C, theplanning can also be confirmed from generated 3D bone models 1000, 1002and 3D implant models 1004, 1006. If the planning is done incorrectly,the reference lines 100, 100′, 900, 900′ will be corrected in the 2D MRIviews to amend the planning. FIGS. 32A-32C and FIGS. 32E-32G are variousviews of the implant 3D models 1004, 1006 superimposed on the 3D honemodels 1000, 1002. FIG. 32D is a coronal view of the bone models 1000,1002.

FIGS. 32A-32G show an embodiment of the POP system disclosed herein. Thealignment of the implant models 1004, 1006 with the hone models 1000,1002 is checked in the anterior view (FIG. 32A), the posterior view(FIG. 32E), the lateral view (FIG. 32B), the medial view (FIG. 32C), thetop view (FIG. 32F) and the bottom view (FIG. 32G).

The flexion/extension between the femur and tibia implant models 1004,1006 and the femur and tibia bone models 1000, 1002 is examined in boththe medial view and the lateral view. For example, FIG. 32B shows thelateral view wherein the knee is shown in full extension or 0 degreeflexion and in its natural alignment similar to its pre-arthritis status(e.g., neutral, varus or valgus), and FIG. 32C shows the medial view ofthe knee in full extension or 0 degree flexion and in its naturalalignment (e.g., neutral, varus or valgus).

FIG. 32D shows the varus/valgus alignment of the knee model 28 m′, 28 m″with the absence of the implants 34 m′, 34 m″. The gaps Gp4, Gp5 betweenthe lowermost portions of distal femoral condyles 302, 303 and thelowermost portions of the tibia plateau 404, 406 will be measured in thefemoral and tibia bone models 28 m′, 28 m″. Gap Gp4 represents thedistance between the distal lateral femoral condyle 302 and the lateraltibial plateau 404. Gap Gp5 represents the distance between the distalmedial femoral condyle 303 and the medial tibial plateau 406. In thevarus/valgus rotation and alignment. Gp4 is substantially equal to Gp5,or |Gp4−Gp5|<<1 mm. FIG. 32D shows the knee model 28 m′, 28 m″ that isintended to restore the patient's knee back to his pre-OA stage.

The IR/ER rotation between the femur and tibia implant models 1004, 1006and the femur and tibia bone models 1000, 1002 is examined in both thetop and bottom views. For example, FIG. 32F shows the top view of thetibia showing the IR/ER rotation between no flexion and high flexion,and FIG. 32G (shows the bottom view of the femur showing the IR/ERrotation between no flexion and high flexion. The stem of the tibiaimplant model 1006 and the surgical cut plane of the tibia implant model1006 provide the information for the IR/ER rotation.

FIGS. 33A-33C show another embodiment of the POP system disclosedherein. FIG. 33A is an medial view of the 3D bone models. FIG. 33B is anmedial view of the 3D implant models. FIG. 33C is an medial view of the3D implant models superimposed on the 3D bone models.

As shown in FIG. 33A, a 3D model of the femur bone 1000 and a 3D modelof the tibia bone 1002 may be generated from the 2D segmentation splinesof image slices and the reference data 100, 900 determined above forverification of the POP. As shown in FIG. 33B, a 3D model of the femurimplant 1004 and a 3D model of the tibia implant 1006 may be generatedbased on the reference lines 100′, 900′ determined above forverification of the POP. The implant models 1004, 1006 and the bonemodels 1000, 1002 are aligned based on the reference lines in a 3Dcomputer modeling environment and the alignment is checked in thesagittal view as shown in FIG. 33C. If the alignment of the bone models1000, 1002 and the implant models 1004, 1006 is not correct, thereference lines 100, 100′, 900, 900′ will be corrected in the 2D viewsto amend the planning.

The knee model 28′, 28″, 1000, 1002 and associated implant models 34′,34″, 1004, 1006 developed through the above-discussed processes includedimensions, features and orientations that the system 10 depicted inFIG. 1A can be utilized to generate 3D models of femur and tibia cuttingjigs 2. The 3D model information regarding the cutting jigs can then beprovided to a CNC machine 10 to machine the jigs 2 from a polymer orother material.

G. Mechanical Axis Alignment

While much of the preceding disclosure is provided in the context ofachieving natural alignment for the patient's knee post implantation ofthe actual physical femur and tibia implants, it should be noted thatthe systems and methods disclosed herein can be readily modified toproduce an arthroplasty jig 2 that would achieve a zero degreemechanical axis alignment for the patient's knee post implantation.

For example, in one embodiment, the surgeon utilizes a natural alignmentfemoral arthroplasty jig 2A as depicted in FIGS. 2A and 2B to completethe first distal resection in the patient's femoral condylar region.Instead of utilizing a natural alignment tibia arthroplasty jig 2B asdepicted in FIGS. 2C and 2D, the surgeon instead completes the firstproximal resection in the patient's tibia plateau region via free handor a mechanical axis guide to cause the patient's tibia implant toresult in a mechanical axis alignment or an alignment based off of themechanical axis (e.g., an alignment that is approximately one toapproximately three degrees varus or valgus relative to zero degreemechanical axis).

In one embodiment, as indicated in FIGS. 34A-35B, the arthroplasty jigs2AM and 2BM may be configured to provide bone resections that lead tonatural alignment, mechanical axis alignment or alignments in betweenthe two. For example, the jigs 2AM and 2BM may have a natural alignmentsaw slot 123 and one or more non-natural alignment saw slots 123′, 123″and 123′″ that may, for example, be one degree, two degrees, threedegrees or some other incremental measurement away from naturalalignment and towards zero degree mechanical axis alignment. The surgeonmay select a two degree deviation slot 123″ based on a physicalinspection and surgical experience.

In one embodiment of the POP systems and methods disclosed herein,instead of superposing the 3D hone models 1000, 1002 to the 3D implantmodels 1004, 1006 in a manner that results in the saw cut and drill holedata 44 that leads to the production of natural alignment arthroplastyjigs 2A, 2B, the superposing of the bone and implant models 1000, 1002,1004, 1006 may be conducted such that the resulting saw cut and drillhole data 44 leads to the production of zero degree mechanical axisalignment arthroplasty jigs or some other type of arthroplasty jigdeviating in a desired manner from zero degree mechanical axis.

Thus, depending on the type of arthroplasty jig desired, the systems andmethods disclosed herein may be applied to both the production ofnatural alignment arthroplasty jigs, zero degree mechanical axisalignment jigs, or arthroplasty jigs configured to provide a result thatis somewhere between natural alignment and zero degree mechanical axisalignment.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

The invention claimed is:
 1. A method of preoperatively planning anarthroplasty procedure on a tibia of a patient, wherein an implant isimplanted on the tibia of the patient as part of the arthroplastyprocedure, the method comprising: identifying on a three dimensionalcomputer model of the tibia a first point at a most distally recessedlocation on a condylar surface of the tibia; identifying on a threedimensional computer model of an implant a second point at a mostdistally recessed location on a condylar surface of the implant;positioning the second point on the three dimensional computer model ofthe implant in a position relative to the first point on the threedimensional computer model of the tibia such that the first and secondpoints match with respect to position in a common coordinate system, thethree dimensional computer model of the implant comprising a distalsurface and a tibial cut plane corresponding to distal surface, theposition of the three dimensional computer model of the implant relativeto the first point on the three dimensional computer model of the tibiabeing reflective of the implant being implanted on the tibia; andautomatically identifying a preliminary position and orientation of aresection of the tibia with the three dimensional computer model of theimplant in the position relative to the first point on the threedimensional computer model of the tibia based on a position andorientation of the tibial cut plane relative to the three dimensionalcomputer model of the tibia.
 2. The method of claim 1, wherein thepositioning of the three dimensional computer model of the implant inthe position relative to the first point on the three dimensionalcomputer model of the tibia occurs in two dimensions.
 3. The method ofclaim 2, wherein the positioning occurring in two dimensions includesprojecting the first point to an axial plane.
 4. The method of claim 1,wherein the matching occurs in two dimensions.
 5. The method of claim 4,wherein the matching occurring in two dimensions includes projecting thefirst and second points to an axial plane.
 6. The method of claim 1,wherein the matching employs iterative closest point matching.
 7. Themethod of claim 1, wherein the identifying on a three dimensionalcomputer model of the tibia a first point includes identifying a firstpoint on the three dimensional computer model of the tibia at a mostdistally recessed location on each of a medial condylar surface of thetibia and a lateral condylar surface of the tibia.
 8. The method ofclaim 7, further comprising identifying on the three dimensionalcomputer model of the implant a second point at a most distally recessedlocation on each of a lateral and medial condylar surfaces of theimplant, wherein the positioning of the three dimensional computer modelof the implant in the position relative to the first point on the threedimensional computer model of the tibia includes respectively matchingthe first and second points.
 9. The method of claim 1, wherein thepositioning of the three dimensional computer model of the implant inthe position relative to the first point on the three dimensionalcomputer model of the tibia includes aligning the first point with amost distally recessed location on a condylar surface of the implant.10. The method of claim 9, wherein the aligning occurs in twodimensions.
 11. The method of claim 10, wherein the aligning occurringin two dimensions includes projecting the point to an axial plane. 12.The method of claim 1, further comprising adjusting the location of thefirst point to reflect an estimated cartilage thickness.
 13. The methodof claim 12, wherein the adjusting of the first point is proximally awayfrom the condylar surface of the tibia.
 14. A method of performing thearthroplasty procedure, the method comprising the preoperative planningof claim 1 and further comprising guiding a surgeon in making an actualresection of the tibia according to the resection of the tibia definedin the preoperative planning of claim
 1. 15. The method of claim 14,wherein the guiding comprises restraining bone removal to a region inthe tibia corresponding to the resection of the tibia defined in thepreoperative planning of claim
 1. 16. The method of claim 15, whereinthe restraining is provided by a slot of an arthroplasty jig matinglycontacting the tibia.
 17. The method of claim 14, further comprisingregistering with the tibia the resection of the tibia defined in thepreoperative plan of claim 1, wherein the registering comprises causinga custom mating region of an arthroplasty jig to matingly contact thetibia.
 18. The method of claim 1, further comprising: adjusting thepreliminary position and orientation of the resection of the tibia toaccount for cartilage thickness.